.migineering 
Library 


UNIVERSITY   OF   CALIFORNIA 

DEPARTMENT  OF  CIVIL  ENGINEERING 

BERKELEY 


December 

Eighteenth 

1922 

Dear  Professor  Derleth: 

I  take  pleasure  in  transmitting  to  you  a 
copy  of  the  Extension  Division  Correspondence  Course 

.3RIALS  OF  ENGINEERING  COHSTRUCTOT,  the  raultigraphing 
of  vrhich  has  Just  teen  oorapleted.   I  thought  that  you 
might  like  to  have  a  copy  in  the  department  files. 

Sincerely  yours, 


professor  C.  Derleth  Jr.,  Dean, 
College  of  Civil  Engineering, 
C  a  m  p  u  s. 


1/IMU 


UNIVERSITY  QF  CALIFORNIA 
EXTENSION  DIVISION. 

Correspondence  Course 


MATERIALS  QF  ENGINEERING  CONSTRUCTION 
Civil  Engineering  8. 

]          By 

C.  T. 


Associate  Professor 

of 
Civil  Engineering. 


A  Course  of  Thirty  Assignments, 
In  Two  •tarts,  8a  and  8b. 


1922 


:oqe.!  • 


. 


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II.  .0 

e;*£loc 


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UNIVERSITY   OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineer ing -Const ruction 

% 

Civil  Engr   -  8.  •       Professor  C.   T.   Wiskocil 

PREFACE 


The  Course   in  MATERIALS  OF  ENGINEERING  CONSTRUCTION  will 
consist  of  30  assignments,    or   lessons,   of  mimeographed  material  which 
will  be   sent   out  by  the  Extension  Division  of  the  University  of 
California.     The  course  will   be  divided   into  two  parts,   designated 
8A  and  8B  ,   each  part  consisting  of  fifteen  assignments.     University 
credit   in  the  amount   of  two  units  will  be  given  on  the  completion 
of  both  parts   of  this  course.     The  textbook  which  is  to  be  used 
is   Johnson's   "Materials   of  Engineering  Construction",   published  by 

Wiley  &  Sons.      It  may  be   obtained  from  the  Associated   Students' 

Union  Bldg. 
Store,   .Student/-,  Berkeley,   California,   for  C6.20,   postpaid. 

Books   on  MaiLKlALS  usually  contain  more   information  than 
is  necessary  to  give  you  a  -.verking  knowledge   of  the   subjects  treated. 
These  books   are  excellent   sources   of  information  and  with  proper 
guidance   they  can    be   used   as  texts.      JOHNSON'S  MATERIALS  OF 
CONSTRUCTION,  which  has  been  used  for  the  past  two  years  at  the 
University  of  California,    is   such  a   oook.      To  use   it   effectively, 
however,    it  was  necessary  to  continually  maintain  the   student's 
interest.      This  was  done  by   informal  talks,    in  which  the   important 
information  was  pointed   out,   and  by  frequent   questions  on  the  es- 
sential  facts  discussed. 

793908 


Civil  Engr.-8.  Page   2. 

Since  university  credit   in  the  Extension  course   in 
MATERIALS  can  be    secured   only  by  passing  supervised   examinations 
similar  to  those   taken  by  resident   students,    it  has  been  decided  to 
use   JOHNSON'S  MATERIALS  OF  CONSTRUCTION  as  the   text-book  and   par- 
allel the   resident-course   still  farther  by  supplying  notes  to  take 
the  place   of  class-room  lectures  and  discussions.     The  purpose  of 
the  notes  which  will  accompany  each  assignment   is  to  assist  you  by 
emphasizing,   explaining,   and   supplementing  the   subject  matter 
assigned   in  the  text.     A -set   of  questions  will  also  be   sent  out 
with  each  assignment.     You  should  test  your  knowledge   of  the  subject 
by  answering  these  questions  without  reference  to  the  notes  or  text- 
book.    At  every  opportunity,  you  should   secure  first-hand   informa- 
tion by  observing  all  examples  of  occurrence,  manufacture,   or   use 
of  the  materials  you  are   studying. 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 
Civil  Engr.   8.  Professor  C»   T-   Wiskocil 

INTRODUCT    ION 


The  purpose   of  this  course   is  to  present   information  con- 
cerning the  mechanical  and  physical  properties   of  the  principal 
materials   of  engineering.     A  knowledge   of  these  properties   is  neces- 
sary for  the   intelligent   selection  and  use   of  materials  for  given 
conditions   or    service  requirements. 

Since  the  adaptibility  and   limitations  of  materials  de- 
pend upon  their  mechanical  and  physical  properties,    it   is  important 
to  know  about  the  modes  of  occurrence,  methods  of  manufacture,   or 
preparation  because  variations   in  these  factors  affect  the  properties. 
Other   subjects  properly  discussed   in  this  course  are:     testing  of 
materials  and  the  fatigue  and  corrosion  of  metals. 

Information  on  materials   is  obtained   from  various   sources. 
Most   of  the  data  on  the  properties  are   compiled    from  the  published 
results   of   investigations   and   researches  while  the  principles   in- 
volved  in  the   occurrence  and  manufacture  are   taken  from  treatises 
on  Botany,   Ceramics,   Chemistry,   Geology,    and   Metallurgy • 

Each  material  will  be  discussed    in  sufficient  detail  to 
bring  out  the  desired   information.      It  would   oe    oeyond  the   scope  of 
the   course   to  exhaustively  treat   each  suoject   or  to  take  up  all 
engineering  materials.      The  course  will   be  given   in  accordance  with 
the   following  outline  : 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 
Civil  Engr  8A-  Professor  C.  T.  VJiskocil. 


Assignment 

1 
2 
3 

4 

5 
6 
7 
8 

9 

10 

11 
12 
13 
14 
15 


Subject 

Mechanics  of  kate rials 
Machines  and  Appliances  for  Testing 
Testing  of  Structural  Materials 
Uses  and  physical  Properties  of  Wood 
Deterioration  and  Preservation  of  Wood 
Mechanical  Properties  of  Wood 
Building  Stone 

Structural  Clay  Products.  Specifications 
for  Paving  Bricks 

Portland  Cement 

Results  of  Tests  on  Cement.  (Natural 
Cement) 

Lime  and  plasters 

Testing  of  Hydraulic  Cement 

Making  of  mortar  and  Concrete 

Mixing,  placing,  and  Curing  of  Concrete 

Proportioning  of  Concrete 


UNIVERSITY  OF  CAllFORNlA.  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 
Civil  Engr  -8B-  Professor  C.  I.  Wiskocil. 


Assignment 
16 
17 
18 

19 
20 
21 
22 
23 

24 
25 

26 
27 

28 
29 
30 


Subject 

Physical  Properties  of  Mortar  and  Con- 
crete 

Permeability  and  Durability  of  Concrete. 
(Portland  Cement  Products) 

Metals  and  Their  Ores.  (Reduction  of  Iron 
from  Its  Ores) 

Manufacture  of  Wrought  Iron  and  Steel 
Manufacture  of  Steel  Shapes 
Formation  and  Structure  of  Alloys 
Constitution  of  Iron  and  Steel 

Properties  of  brought  Iron.  (Properties 
of  Steel) 

Effects  of  Heat  Treatment  of  Steel 

Effects  of  Mechanical  Work  on  Steel. 
(Effects  of  Temperature  on  Mechanical 
Properties  of  Metals) 

Alloy  Steels 

Cast  Iron  and  Malleable  Cast  Iron 

Non-ferrous  Metals  and  Alloys 

Fatigue  of  Metals 

The  Corrosion  of  Metals 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 
Civil  Engr  8A.  Professor  C.    T.   Wiskocil 

Assignment   1 
MECHANICS  OF   MATERIALS 


Reading  assignment  ;-      Johnson's  Materials   of  Construction,   Chapter    I, 

pages    1-48. 


Preliminary  :-  Before  studying  the  various  materials  it  is  advisable 
to  have  a  general  knowledge  of  the  effects  of  stress  and  deformation. 
The  subject  of  internal  forces  and  deformations  is  ordinarily  called 
MECHANICS  OF  MATERIALS.   Chapter  I  is  a  condensed  treatment  of  this 
subject  which  is  a  complete  course  of  study  in  itself.  The  assign- 
ment, therefore,  will  not  be  studied  intensively.  Only  that  infor- 
mation which  is  necessary  for  a  thorough  understanding  of  the  prop- 
erties of  the  materials  to  be  studied  later  -will  be  discussed.   T'-r 
The  directions  ''study"  in  these  notes  means  that  you  should  know  the 
contents  of  the  immediate  subject  and  be  able  to  stace  in  your  own 
words  what  you  have  studied.   Do  this  with  each  paragraph. 

Study  Article  1  in  connection  with  the  following  notes: 

Stress;-   Stress  is  the  force  at  a  point  or  plane  in  a  body  or  the 
force  between  contiguous  surfaces  of  two  oodies.   The  forces  or  loads 
producing  the  stresses,  or  the  stresses  themselves,  may  be  represent- 
ed by  arrows  and  the  bodies  acted  upon  by  small  rectangles-   Thus  in 
Figure  1  the  weight  is  suspended  from  the  support  oy  the  rod  as 
shown.   The  situation  could  be  illustrated  as  in  Figure  2,  the  arrows 


Civil  Engr  -8.  Assignment  1.  Page  2. 

indicating  the  forces  and  the  directions  in  which  they  act  upon 
the  body.   If  the  weight  is  100  Ib.  the  total  stress  in  the  rod  on 
the  Section  A  —  A  is  100  Ib.  irrespective  of  the  size  of  the  rod 
Plane  sections  are  always  taken. 


Figure  2. 


Figure  1 


Unit  Stress.  Unit  stress  or  intensity  of  stress  is  obtained  by  divid- 
ing the  total  stress  by  the  entire  area  of  the  section  on  which  it 

P 
acts  or  over  which  it  is  distributed.   Intensity  of  stress   S  -  — 

A 

where  P  is  the  stress  and  A  is  the  area.   In  mechanics  it  is 

usually  measured  in  pounds  per  square  inch,  which  is  abbreviated 

P 

Ib.  per  sq.  in.,   Ib./  in.,   or  $/£j"-   S   is  the  actual  intensity  of 

stress  only  when  the  stress  is  uniform  over  the  section.   In  the  case 
of  a  varying  stress,   S  is  the  average  intensity  of  stress. 
Example  -  A  body  is  subjected  to  a  force  of  1,000  Ib.   Its  dimensions 
normal  to  the  direction  of  the  force  are  1"  by  2".  What  is  the  inten- 
sity of  stress? 


Civil  Engr   8.  Assignment   1.  ..  Page  4. 

divided  by  the   length  which  is     tan  0;  this   is  also  an  abstract 
number. 

The   following  notes  explain  Article  2  which  should  be  carefully  stud- 
ied. 

Kinds  of  Stresses;-     '.;.wo  classes  of  stresses  are  usually  considered; 
(a)    simple   or  uni-directional   stresses  and      (b)   combined   or  bi-dir- 
ectional  stresses.      The   simple   stresses  are  tension,   compression, 
and   shear  which  includes  simple  torsion.      The  combined   stresses  are 
tension  with  tension  or  compression,   compression  with  compression, 
and   shear    (torsion)     with  tension  or  compression. 

Tension 

A  body  subjected  to  an  axial  pull  is  in  tension.  The 
forces  act  in  the  same  line  and  away  from  each  other  tending  to  pull 
the  body  apart.   The  section  on  which  the  forces  act  is  taken  perpen- 
dicular to  the  direction  of  the  force,  as  A  --  A  in  Figure  1, 
which  shows  a  rod  in  tension.  Examples  of  bodies  in  tension  are;  tie 
rods,  guy  wires,  belts,  and  violin  strings. 

Compression 

When  axial  forces  act  in  the  same  line  and  toward  each 
other  the  body  is  in  compression.   The  section  is  taken  as  in  the 
case  of  tension.   Figure  4  represents  a  body  in  compression,  Ex- 
amples of  bodies  in  compression  are;  posts  supporting  floors  or  other 
loads,  table  legs  and  connecting  rods  in  single-acting  internal  com- 
bustion engines. 


Civil  Engr.    8.  Assignment    1.  Page   5. 

Shear 

When  the  forces  act  in  parallel  lines  either  toward  or 
away  from  each  other,  but  sufficiently  close  so  that  there  is  no 
bending,  the  body  is  in  shear.   The  section  is  taken  parallel  to 
the  forces  (note  that  this  is  different  than  in  the  case  of  tension 
and  compression).   Shear  is  illustrated  oest  by  the  stress  in  a  bolt 
or  rivet  holding  tv;o  plates  from  sliding  on  each  other  as  in  fig- 
ure 6. 


U 


The  particles  in  a  body  under  a  twisting  moment  or  torsion,  as  a 
shaft  transmitting  power,  have  a  tendency  to  slip  on  each  other;  the 
stress  produced  is  simple  shear.  Simple  torsion  rarely  occurs,  it  is 
usually  combined  with  tension  or  compression. 

Combined  Stresses 

Flexure  is  classed  under  combined  stress.   In  simple  flex- 
ure or  bending  the  fioers  on  the  concave  si^e  of  the  body  are  short- 
ened and  are  therefore  ii  compression  whereas  on  the  convex  side/ 
they  are  lengthened  anc  are  in  tension.   The  stresses  across  the  body 
vary  from  tension  to  compression;  at  some  point  between  these  ex- 
tremes the  stress  is  zero  -  neither  tension  nor  compression.   Flex- 
ure is  usually  produced  by  transverse  loads  which  produce  sihear  in 
addition  to  the  stresses  of  simple  bending.   A  loaded  beam  is  an  ex- 
ample of  flexure.   A  body  may  be  subjected  to  flexure  and  axial  stress, 
This  combination  of  simple  stresses  is  illustrated  in  the  rafters  of 


Civil  Engr.  8.  Assignment  1. 

an  A-frame  roof.   Shear  (torsion)  may  be  combined  with  compression 
as  in  the  case  of  a  shaft  of  a  vertical  turbine.   Shear  may  also  be 
combined  -with  flexure  as  in  a  line  shaft  with  power  taken  oi'f  by 
belts  between  the  hangers  or  bearings. 

Loads:-  The  ability  of  materials  to  sustain  loads  depends  upon  the 
manner  in  which  they  are  applied.  Loads  u.ay  be  class  if  ied  as  static 
and  dynamic.  Static  loads  include  dead  loads,  whi'.ch  are  sometimes 

called  stationary  or  permanent  loads,  and  gradually  applied  loads, 
as  in  the  case  of  a  testing  machine  where  the  load  varies  from  zero 

to  a  maximum,  during  the  period  of  the  test.  Dynamic  or  suddenly- 
applied  loads  may  be  applied  with  or  without  shock  or  impact.   They 
may  be  applied  occasionally  or  continuously.   In  the  latter  case 
they  would  be  called  alternating  or  repeated  loads,  depending  upon 
whether  the  stress  changed  in  character  or  was  simply  reapplied  in 
the  same  manner.   In  either  case  their  effect  -would  be  discussed 
under  the  subject  of  FATIGUE. 

Elastic  and  Plastic  Bodier;:-  Study  Article  3.   Materials  may  be 
classified  as  brittle  and  ductile.  Both  classes  are  described  in 
this  article.   The  term,  ultimate  strength,  is  alsc  defined.   Fre- 
quently the  maximum  unit  strtss  carried  by  a  material  is  siraply 
called  its  strength;  ultimate  strength  is  a?.wa^  s  uieant.   It  should 
be  understood  that  the  kind  of  stress  must  be  specified  because  a 
material  may  have  different  tensile  and  compressrvc  strengths. 

Modulus  of  Elasticity :-   Study  Article  4,  as  it  is  vsry  important. 
Remember  that  the  modulus  of  elasticity  is  always  denoted  by  E 


Civil  Engr.    8.  Assignment   1.  Page   7. 

and   that  although   it   is  a   ratio  of  unit   stress  to  unit  deformation 

it    is  measured    in  Ib.    per   sq.    in.      because 
P 

E     =         A       -       Ib.    per   sq.    in. 

AT  — =       Ib.    per   sq.    in.  since 

in.    per      in. 
Li 

the  denominator   is  unity.      E     is  the  measure   of  the   stiffness   or 
flexibility  of  a  material.      Fortunately  the  modulus   of  elasticity  of 
all  kinds   of  steel  is  very  nearly  the   same,   namely     30,000,000  Ib. 
per    sq.    in.      E     for  concrete   is  aoout   1/15  that   of   steel,    or 
2,000,000  Ib.    per   sq.    in.    and  for  v;ood   it   is  about   1,500,000  Ib.    per 
sq.    in. 

/ 
Poisson's  Ratio:-       This   ratio   (pronounced     pwa   sonz   )      is  about 

-   1/4  for  steel  and   about   -   1/8  for  concrete.      The   negative    sign   in- 
dicates that   it   is   opposite    in  character     to  the   principal  deforma- 
tion.    As   explained    in  Article   5,    it   is  the   ratio  of   lateral  to 

longitudinal   deformation.      If  a   block  of   steel   is  compressed    its 

/  / 1 

increase  in  width,  measured  perpendicular  to  the  direction  of  the 

applied  force,  will  be  about  1/4  of  its  decrease  in  length.   These 
relations  hold  only  within  the  elastic  limit  of  the  material  and  the 
changes  are  very  small,  requiring  delicate  instruments  to  measure 
the  amount  of  deformation.   Poisson's  Ratio  is  of  importance  in 
theoretic  discussions  in  MECHANICS  OF  MATERIALS,  and  of  practical  im- 
portance in  the  manufacture  of  guns. 

Volumetric  Deformation:-   Article  6  is  not  important.   It  is  inter- 
esting to  note,  however,  that  a  body  subjected  to  tension  v;ill 


Civil  Engr.    8.  Assignment   1.  Page   8. 

slightly   increase    in  volume.      For   example,   a  piece    of   steel  4"  by  4" 
by  60"  under  a   tension   of  430,000   Ib.    will   increase   aoaut     0.29  cubic 
inches   in  volume   or  about  three  hundredths  of  one   per  cent. 

Shearing  Modulus   of  Elasticity :-        Shearing  modulus   of  elasticity   is 
explained    in  Article   7.      It   is  sometimes  called  the  modulus     of 
rigidity  and    is  measured    in  Ib.    per  sq.    in.          For   steel   it   is  about 
2/5   of  E_. 

General  Properties   of  Laterials :-       Study  Article   8.     The  general 
properties  described    in  this  article  are    important  and  "will  be  re- 
ferred  to  during  the   discussion  of  the   various  materials. 

Strength  is  obviously  a  property  that  materials  must  pos- 
sess so  as  not  to  rupture   or  fail  under   stress.      Frequently   strength 
is  the  principal  consideration,   as   in  chains,   crowbars,    stern-frames 
of  ships,   and  cranes.      In  other  cases  strength  is   of  secondary   im- 
portance and   some   other  property,   such  as   stiffness,   governs  the 
selection  of  the  material.      Wood  because   of   its  low  degree   of  stiff- 
ness will  yield   under    impact   and    for  that   reason   (besides    its   light 
weight)    it    is  used   by  seme  manufacturers    in  the   construction  of 
automobile  frames.      It  also  makes  the  best  railroad  ties   for  the   same 
reason.      In  other  machines  and   structures  stiffness   is  the  prime 
requisite. 

Ductility  and  Malleability  are   closely  allied.      Toughness 
and  brittleness  are   antonyms.      Toughness    is   the   ability  to  withstand 
impact   stresses.      It    is  dependent  upon  both   strength  end   deformation. 
Two  bodies  having  the    same    strength,   as   ordinarily  determined,   can 


Civil  Bngr.    9.  Assignment   1.  Page   S. 

have  different   lengths  providing  their   areas   are  the   same.      If 
these  t?;o  bodies   of  the   sane  area  are   subjected  to  impact  the   longer 
one  -will  withstand  the   greatest   shock.     With  the   same  cross-section- 
al area  the   toughness    increases   in  direct          proportion  with  the 
length.     For  most  mate-rials  the  energy  of  rupture,  which  is  the 
are?,  under  the  stress-deformation  curve,    is  an  index  of  the  toughness 
(see  the  third   papagraph,  which  begins  about  the  middle   of  page  42, 
of  Article   37).     The    longer  piece  will  undergo  greater  deformation 
and  will  therefore  have  a   greater   area  under  the  curve  even  though 
the  maximum  strength  is  the   same  as  the   shorter  piece.      In  Figure  3 
page   8,   the   steel  having  a  tensile    strength   of  75,000  Ib.   per   sq.    in. 
is  tougher  than  the   105,000     Ib.   per   sq.    in.    steel.     That   is,    it  has 
a  greater   resistance  to  rupture  under   impact.     A-s   shown  in  Figure  4, 
on  page   9,  the   105,000  Ib.   per  sq.    in.    steel  has  a  higher   elastic 
resistance  to  impact.      Ix,  will  withstand  permanent  distortion  under 
greater   impact   stresses  than  the    steel  having  a    strength  of  75 ,,000  Ib, 
per   sq.    in.  ,    because    :.t  hc.s   n   greater  proportional    or    elastic    limit 
and   consequently  a   greater   -  rea   under  thrt   part   of  the    stress- 
deformation  curve.      Material  v;ith  a  high  elastic    limit    is  used   for 
springs  while  meteri^l  with  less  strength  but  more   ductility    is  used 
for  machine  parts   subject   to   occasional  heavy   impact   such  as  car 
couplings  are.     Elasticity  and   plasticity  were   defined    in  Article   3. 
Uniformity  of  properties   is   very  desirable.      Some  mater- 
ials  such  as  steel  can  be   produced  with  a   high  degree    of  uniformity, 
whereas  the  properties      -  "  of     wood   vary  over  vide    limits. 


Civil  Bngr.    8.  Assignment   1.  Page    10. 

Durability   is  probably  one   of  the  most   inroortant  proper- 
ties and,    for   permanent   construction,    it  must  always  be   considered 
because  certain  materials   are  very   susceptible  to  decay  or  deterior- 
ation.     Destructive   agencies  such  as  corrosion,   bacteria,   fungi, 
electrolysis,  mechanical  v;ear,  chemical  Action,   ant?   fire  act   on 
materials  used   in  engineering  construction. 

Materials  under  tensile   stress;-        Study  Articles  11  to  16  very  care- 
fully.    The  stress-deformation  diagram  is   important.     Read  Article 
111  and   see  Figure   12   on  page  476  and  Figure   9   on  page  620  for 
typical  examples  of   stress-deformation  diagrams.      Note  that  the^ulti- 
mate   strength  is   obtained  by  Dividing  the  maximum  stress  by  the 
original     cross-sectional  area. 

Read  the   following   in  connection  with  your   study  of 
Article    11. 

Significance   of  elastic   limit  ;-       The  elastic    limit  of  a  ductile 
material,  when  used    in  machines  or  machine  parts  which  cannot  be  dis- 
torted,   is  practically   its  ultimate    strength  in  both  tension  and 
compression.      Very  s.r,?ll  permanent  distortion  will  cause   serious 
damage  to  machines   of  precision.     A  brittle  materiel  has  no  well  de- 
fined  elastic      limit  when  that  term  is  used   to  include  the  yield 
point,   and    its  ultimate   strength  is  the  most  reliable  criterion     of 
strength  for  static   loads.      Brittle  materials  are  not  used   in  direct 
tension  or  where  they  would  be   subjected  to  shock  or   impact  stresses. 
Materials  under  compress  ive   stress:-     Study  Articles   17,    18, 


that  part   of   19  which   is   given  on  page   14.     Reed    over  the   rest   of  the 


Civil  Engr.  8-  Assignment  1. 

article.   Remember  that  short  blocks  of  brittle  materials  under  com- 
pression fail  in  shear  on  a  plane  of  rupture  \vhich  has  an  angle  of 
about  35  degrees  with  the  direction  of  the  conpressive  force.  Reac 
Article  20.   Study  Article  21  up  to  Euler's  Formula. 
Materials  under  shearing  stress;-    The  nature  of  shearing  stresses 
have  been  described.  Read  Article  23  up  to  equation  16  and  study  the 
last  paragraph  in  Article  24  on  page  24. 

Materials  under  cross-bending  stress:-    Study  the  first  paragraph 
of  Article  25  and  read  the  rest  of  the  article.  Read  Article  26. 
Study  Article  27,  omit  ing  the  last  paragraph. 

Formula  20  on  page  25  may  be  written     S  ~  Ml   where 
S  is  the  modulus  of  rupture.   This  is  an  important  quantity.   It  is 
the  nominal  fiber  stress  at  a  definite  point,  that  of  greatest  stress. 
Remember  that  the  stress  varies  across  the  section  of  a  beam..  Modu- 
lus of  rupture  is  mer.sured  in  Ib.  per  sq.  in.  and  may  be  tension  otT 
compression.   M  is  the  moment  in  inch  pounds,  c   is  the  distance 
from  the  neutral  surface  to  the  extreme  fiber  in  inches,  and  I  is 
the  moment  of  inertia  of  the  section,  sbout  the  neutral  axis,  in 

inches  to  the  fourth  power.   Therefore    S  =  .. in"  *]?•  *  in>   = 

in 

Ib.    per   sq.    in.        Modulus  of  rupture   is  not  the  actual   stress  because 
it   is  used  v:ith  the  ultimate  value   of  M       whereas  the   formula  was 
developed    on  the  assumption  that  the   elastic   limit  rras  not   exceeded. 
It   is   sufficient  to  remember  that  the  actual  stress   is   less  than  the 
modulus   of  rupture.      Modulus   of  rupture    is  easily  computed   and    is 
always  given  as  the   cross-breaking  or  transverse   strength  of  materi- 
al  in  question.      Study  Article   28,    omiting     the   derivation   of  the 


Civil  Engr.   8.  r  Assignment  1.  jo>^  _  i.fc. 

intensity  of  shearing   stress,   and  the   last  two  paragraphs.     Remem- 
ber that  wooden  beans  must  be   inventigatad   for  horizontal   shear. 
This   is   sometimes  called   longitudinal  shear.      Or.it     Articles  29  to 
32   inclusive. 

Resilience:-     Under   this    subject   study  only  Article   33  and   the  third 
paragraph  of  Article  37,      omit  ing  the  remainder   of  the  chapter. 


Civil  Engr.    8.  Assignment   1.  pagr   1;'. 

Reference  Books  on  Mechanics  of  Materials. 

Elementary  texts-. 

Kottoanp,   J.    P.    STRENGTH  OF  MATERIALS,   Wiley  nnrt  Sons, 

Murdock,  H.  E.  ,    STRENGTH  OF  MATERIALS,  Wiley  and  Sons, 

Smith,  H.  E.  ,        STRENGTH  OF  MATERIALS,  Wiley  and  Sons,    1914. 

Slocum  S.  E.*     RESIST/^CE   OF  MATERIALS,  G-inn  and  Co.,   1014. 

More  oonprehensive  texts : 

Boyd,   J.  E.,     STRENGTH  OF  MATERIALS,     McGraw  -  Rill,     l**f» 
Fuller  and   Johnson,     APPLIED  MECHANICS  Vol.    II,  Wiley  and  Sons 

Merriman,     MECHANICS  OF  MATER IALS,  Wiley  and  Sons, 

Merely,     STRENGTH  OF  MATERIALS,     Longmans,   Green  %  Co, 

London, 


Civil  Engr.    8.  Questions  to  Assignment   1.  page   14. 

Answer  all  questions   submitted  to  you  as  clearly  as  pos- 
sible.     Do  not   go   into  detail  unless  details  are   requested,   "but  do 
not  fail  to  answer  all  parts   of  each  question  completely.     Arrange 
your  answers  neatly.      Use   a  typewriter   if  svailable. 

1.  Define   intensity  of  stress,  unit  deformation,  modulus  of  rupture 
and  modulus   of  elasticity.     Note:     Always  give  the  units   in  which 
the  quantities  are  measured. 

2.  Define   stiffness,   toughness,   and   ductility. 

3.  Can  stiffness  be  measured  quantitatively?     (If  no  other   infor- 
mation is  given  always  answer   a  question  of  this  type  as  completely 
as  possible,   not   simply  by  yes  or  no.) 

4.  The  diagram  on  page   10,    in  the  text,  was  obtained   from  an  actual 
test   in  which  the  load  was   applied  continuously   increasing  from  zero 
to  its  maximum  value  as   indicated.     Was  the   so-called  elastic   limit 
determined?     (Do  not  read  the  description  to  answer  this  question, 
you  should  know  the  answer    if  you  have   studied   the  assignment.) 

Why   is  the   point    indicated  the  most  probable  value   of  the   elastic   1  * 
limit? 

5.  what   is  the  unit    stress   in  a  rod  having  an  area  of  1/2  sq.    in. 
when  subjected  to  a  stress   of  8,000  lb.?  Ans.    16,000  Ib. 

6.  What   is  the   allowable   pull  on  a   1"  diameter   steel  bolt   if  the 

allowable    intensity  of   stress   is   16,000  lb.    per   sq.    in.? 

Ans.      12,600  lb. 

7.  The  head   of  a   1"  diameter  bolt   is  5/8"  thick.     When  the  bolt 
is   subjected  to  a  pull  of  15,000  lb.   what   is   the  unit   shearing 


Civil  Engr.  8.      Questions  to  Assignment  1. 


stress  tending  to  strip  the   head   from  the  bolt?     .'aAns.    7,600  Ib. 

per   sq.    in. 

8.  Would  the  chattering  of  a  machine  tool  (caused  by  bending  of 
the  tool)  be  diminished  by  making  it  of  stronger  steel? 

9.  Which  bolt  -  one  left  full  site  or  one  turned  down  to  the  di- 
aneter  at  the  base  of  the  threads  -  will  sustain  the  greatest 
impact  loading? 

10.  Name  the  kinds  of  stress  developed  in:   (a)  an  inflated  tire 
casing,   (b)  the  connecting  rod  of  a  double  acting  pump,  (c)  a 
key  in  an  axle  shaft,   (d)  stud  bolts  holding  on  a  man-hole  in  a 
pressure  tank. 

11.  Prepare  a  list  of  structures  or  machines  in  which  the  var- 
ious properties  listed  below  govern  the  selection  of  the  material 
to  be  used  : 

(a)  Strength  (d)  Toughness 

(b)  Stiffness          (e)  Hardness. 

(c)  Flexibility 

12.  Prepare  a  list  of  structures  or  machine?  vhioh  are  liable  to 
occasional  overloading. 

13.  Name  several  structures  or  machines  that  could  be  mads  of 
brittle  materials. 

14.  What  kind  of  stress  exists  at  the  neutrel  surface  of  a  load- 
ed beam? 

15.  What  kind  of  stress  exists  in  the  fibers  on  the  leeward  side  of 
a  flag  pole  bent  by  the  wind? 


UNIVERSITY  OF  CALIFORNIA.  EXTENSION  DIVISION" 

Correspondence  Courses 
Materials   of  Engineering  Construction 
Civil  Bngr,    S.  professor  C.   T.  Wi.skocil 

Assignment  2. 

MACHINES  AND  APPLIANCES  FOR  TEST  ING 

Reading  assignment;*       Johnson's  Materials   of  Construction,  Chapter 
II,   pages  49-96. 

Preliminary:-       In  a  comprehensive  study  of  the   important  materials 
of  engineering  construction,    such  as  we  are  making,    it   is  desirable 
to  have  a  knowledge   of  the  machines  and  appliances  used   in  determin- 
ing the  various  properties   such  as  strength,  elasticity,  and  tough- 
ness.     If  properly  studied,  this  chapter  will  eive  yo\i  the  necessary 
information  without  an  actual   inspection  of  a   testing  laboratory. 
There  are  testing  machines   in  'the  San  Francisco  Bay    region,  Los 
Angeles,   Sacramento  and  Fresno  -  possibly  in  other  California  cities, 
Make  an  effort  to  witness  an  actual  test  performance.      If  you  should 
visit  a   laboratory  do  not  expect  to   see  all  the  machines  and  appli- 
ances described   in  this  assignment.      Probably  no  laboratory  in  the 

i 
country,   not   even  the   one    in  the  Bureau  of  Standards  at  Washington, 

b.C.  ,   contains  all  of  them. 

TESTING       MACHINES 

The  discussion  of  testing  machines  constitutes  the  first 
part   of  the  assignment.     A.  testing  machine    is  defined   in  Article  42; 
in  general,    it  must  provide  means  for    (a)   applying  the   load      (b)  mea- 
suring  the    load     and    (c)   holding  the  test   specimen.     A  testing 


Civil  Bngr-8.  Assignment  £.  Page   2. 

machine    is  not  necessarily  a  costly  device   like  those    illustrated 
in  the  te;:t  book;   it  may  be   a  simple  wooden   lever  arrangement     with 
the    load,   a  bucicet  of  aand   at  the  end    of  the   long   lever,   such  as   is 
used    in  the   field  testing  of  drain  tiles.      Testing  machines  vary 
in  capacity  from  the    10,OUC,OCC   lb.   machine    shown  on  page   56  to 
er.aH  tension  machines  for   testing  faoric,    or  briquette-testing 
machines   like  the   ones  shown  on  page   396.      There  are     also  various 
types   of  machines  which  will  now  be  discussed    in  detail.      In  general 
all  testing  machines  must  be  both  accurate  and   sensitive. 

Universal  Testing  Machines 

Classes  jsfjaniversal  teeting  machines:-       Study  Article  43.     Univer- 
sal testing  machines  may  be  divided   into  two  classes,    (a)  vertical 
and    (b)   horizontal.     Both  of  these  classes  may  be  divided    into  two 
groups  based  upon  the  method   of  applying  the   load;   namely,   screw- 
gear  and  hydraulic.      Hydraulic  machines  may  be  either  plain  or   of 
the  Emery  type.     As  a  class  universal  machines  &re   in  most   general 
use   in  the  United   States,  probably  because   of  their  adaptibility. 
They  are  mostly  the  vertical  screw-gear  type  either   of  Olsen  or 
Riehle  make,  both  of  which  will  be  described   later.     Weighing  devices 
used    in  testing  machines  are   levers,   gages,   and  manometers.      The 
Olsen  and  Riehle  machines  use  the   lever  system. 

The   advantage   of  the   horizontal  machine,   besides  the   one 
riven  on  page   50  in  Article  43,    is   the   ease  with  which   large   speci- 
mens  can  be   put    in  place.      The  principal  disadvantage,   as   indicated, 
is  the  bending  of  the   specimen  due  to  its   own  weight,      It  also  takes 
up  a   large  amount   of  floor  space. 


Civil  Engr-8.  Assignment  2.  Page  3. 

General  conditions  which  should  jbts  obtained  in  universal  machines;- 


The  principal  requirements  are  accuracy  and  sensitiveness.   Accuracy 
is  insured  as  indicated  in  paragraph  1,  the  second  sentence  in 
paragraph  2  and  the  first  sentence  in  paragraph  3  or  Article  44. 
paragraphs  1  and  6  of  this  article  refer  to  sensitiveness.   The 
last  sentence  of  paragraph  7  and  paragraph  10,  with  those  already 
given,  are  the  important  ones  of  the  article. 

Olsen  testing  machines;-  Study  Article  45.   The  essential  parts  of 
the  Olsen  machine  are  shown  in  Figure  1.   These  are  usually  four  and 
three-scret;  machines.   The  screws  referred  to  are  the  main  ones 
•which  move  the  cross-head.   In  this  machine  the  screws  do  not  rotate 
on  their  axes,  but  move  the  cross  head  to  which  they  are  attached 
by  the  axial  motion  given  to  them  by  the  rotation  of  the  geared  nuts 
through  which  they  pass.   The  geared  nuts  bear  against  the  frame  of 
the  machine.  The  weighing  mechanism  is  shown  diagramatically  in 
Figure  3.  Note  that  when  the  scale  beam  is  in  balance  the  position 
of  the  poise  -weight  indicates  the  amount  of  the  load.   It  resembles 
the  usual  Fairbanks  platform  scale.  The  purpose  of  the  counter- 
weight is  to  counteract  the  unbalanced  weight  of  the  various  levers 
in  the  system. 


Civil  Engr-6 


Assignment   2 


Page  4 


-* 

II 

II 

1 

<\ 

-- 

-- 

i 

s 

X 

i 

^ 

— 

- 

-- 

Upper  or  Fixed  Head 
- --Position  of  Tensile   Specimen 


<r\ Main  Screv/s  (Do  not  twist) 

---Position  of  Compression  or  Cross- 
Bending  Specimen 

-•Weighing  Table,  rests  on  Levers 
^-Weighing  Levers 

Machine  Bed  or  Frame 


-Threads  on  inside  of  gear  hub  for 

Main  Screws 


-Main  Drive   Shaft 


Figure   1, 


Civil  Erigr-8 


Assignment  2 


Page  5 


-•--Position  of  Tensile   Specimen 

--Threads  in  Cross  Head  for  Main  Screws 
--Cross  Head 

•-•Main  Screws  -  Revolve  to  move  Cross  Head 


...Position  of  Compression  or   Cross. 

Bending  Specimen 


--  Weighing  Table 


Lever   System 

--•Machine  Bed  or  Frame 
:<~Main  Drive   Shaft 


Figure  2 


Counter 
Weight 


m 


ffa 


Frame 


-Scale  Beam 


*v_  Frame 


d — £ 

^Movable  Poise  Weight 


mThrn 
r> 


-Frame 


Figure  3 


Civil  Engr-8  Assignment  2,  Page  6. 

Riehle  testing  machines ;-     Study  Article  46,      It  describes  the 
liiehle   (pronounced  r8   lay)  testing  machine.      This   is  the  principal 
competitor   of  the  Olsen  machine.     Figure  2  shows  the  essential 
pfirts  of  the  Riehle  machine.      It   is  a  two-screw  machine.      The  cross- 
head   is  threaded  to  receive  the  main  screws  which  revolve  and  cause 
it  to  move.      The  main  screws  revolve  without  axial  motion.      The 
weighing  mechanism  is   of  the   eatue  design  as  the  'Olsen. 
The  Emery  testing  machine;-       Study  Article  47  and  Figure  4   in  the 
text,     The  wide   range   in  capacity  and    sensitiveness  of  this  type  of 
machine   is   illustrated  by  the  footnote   on  page   54.     A  high  degree 
of  accuracy   is  not  always  necessary.      The  Emery  machine   is  made  to 
order  and   is  very   expensive.     Note  that  the   load   is  applied  to  one 
end   of  the   specimen  by  the  usual  hydraulic  press  which  can  have 
friction  of  any  amount   or  variation  without  affecting  the   load  which 
is  measured  at  the  other  end  of  the  specimen  by  the  pressure   in  a 
completely  closed  chamber.     There  are  two  of  these  chambers  or  cap- 
sules,  one  to  take  the  full  load   on  the   specimen  and  another,    of 
smaller  size,   connected  to  it  by  hollow  tuoing.      The   smaller  capsule 
actuates  a   lever   system  similar  to  Figure   3   (in  the  notes)  which 
measures  the   load   on  the  capsule.      The    liquid   in  the  capsules   is 
incompressible,   therefore  there   is  no  friction.      The  diaphrans  have 
only  very  small     exposed   surfaces   and  can  therefore  be  made   of  thin 

material.      In  the  Emery  weighing  levers  the   fulcra  consist   of  thin 

in 
plates    (in  tension),  whereas/  the   Olsen  and  Riehle   levers,   the 

fulcra  are   knife  edges   (in  compression).      The  Emery   lever   system  is 
the   more    sensitive. 


Civil  Engr-8.  Assignment  2.  Page  7. 

Tension  Testing  Machines 

This  type  is  not  mentioned  in  the  text  book  but  there  are  ma- 
chines which  will  test  only  in  tension.   In  construction  and  operation 
they  are  similar  to  the  Olsen  and  Riehle  universal  testing  machines. 
A  machine  for  testing  briquettes  in  tension  is  shown  on  page  396.  Ma- 
terials frequently  tested  in  tension  are  wire,  various  kinds  of  fabric, 

leather  and  paper. 

Compression  Testing  Machines 

Study  Articles  48  and  49,  Read  Article  50,  remember  that  the 
largest  machine  has  a  capacity  of  ten  million  pounds  in  compression 
only.   It  is  a  hydraulic  machine  and  the  screws  (shown  in  Figure  6  in 
the  text,  page  56)  are  merely  for  changing  the  position  of  the  cross- 
head  . 

Transverse  Testing  Machines 

Beams  of  wood,  concrete,  and  steel  are  tested  in  this  type  of 
machine.  Study  article  51  and  Figure  9  together  with  the  text  referring 
to  it  on  the  middle  of  page  59.  Read  Article  52.   In  the  cross-bend- 
ing test  of  cast  iron  which  is  made  on  the  machine  illustrated  in  Fig- 
ure 9,  page  59,  the  bending  moment  is  a  maximum  under  the  load.   The 
span  is  usually  12  inches.   The  other  type  of  transverse  loading  is 
illustrated  on  page  202,  Figure  2,   It  is  known  as  the  third  point 
loading,  the  beam  being  divided  into  three  parts,  usually  equal. 
Equal  loads  are  applied  at  equal  distances  from  the  ends  of  the  beam. 
The  bending  moment  between  the  loads  is  constant  and  the  shear  is  zero. 
This  is  a  more  desirable  condition  than  that  obtained  by  the  center 

loading. 

Cold -Bend  Testing  Machines 

Read  Articles  54  and   55.      The  cold   bend  test   is  usually  used 
for  various  kinds   of  steel,    both  rolled   and  cast.      The  bend  test   is  a 
very   important   one  for   steel  to  be  used   for  reinforced-concrete. 


Civil  Engr-8.  Page  8. 

Torsion  Testing  Mac nines 

The  torsion  test   is  most  satisfactory  for  testing  the 
shearing  strength  and   elasticity  of  ductile  materials.     Torsion  can- 
not be  put   on  a  specimen  in  a  machine   of  the  universal  type,      it 
takes  a  special  form  of  machine   such  as   shown  in  Figure   15  page  63. 
Torsion  test   specimens  are  usually  circular   in  section,   either 
hollow  or   solid.      Read  Article   57. 

Impac t  Testing  Machines 

TJber impact  test   is  used  to  determine  the  amount  of  energy 
(measured   in  foot-pounds  or   inch-pounds;  necessary  to  stress  a 
specimen  up  to  its  elastic   limit   or  to  rupture   it.     The  machine 
shown  in  Figure   19,  page  66     is  used  by  the  United  States  Forest 
Service  to  test  the  toughnesfe  of  -wood.     The  usual  impact  test     is 
in  flexure  but   impact  compression  and  tension  tests  can  be  made    in 
the  Turner  machine.      The  pendulum  t^;pe   of   impact  testing  machine 
subjects  the   specimen     to  flexural   stresses;      it  can  be  arranged 
to  test  a   specimen  in  tension.      If  ductile  meter ials  are  tested   in 
impact-flexure  the    specimen   is  usually  notched  so  as  to  localize 
the   stress  and   insure   failure.      Study  Articles  58,   59,   and  60  in 
the   text. 

Endurance  Testing  Machines 

Endurance    or   repeated    stress  testing  machines   in  common 
use  are   of  two  general  types.      The  Upton-Lewis  machine    (not  shov;n 
in  the  text)   and  the  Kommers  machine    (shown  in  Figure  26,   page  72) 
produce  flexural  stresses  by  simple    bending  of  the   specimen,  where- 


Civil  Sngr-8.  Assignment  2  Page  9. 

as  the  White-Southtr  machine  produces  flexural  stresses  by     rotating 

a   loaded   specimen  (The  machine   is   shown  in  Figure   25,   page  71).      In 
both  types  of  machines  there   is  a  reversal  of  stress   ^from  tension 

to  compression)   as  the   specimen  is  bent  or  rotated.     The  Up ton- Lewi s 
machine  works  best  at   stresses  aoove  the  elastic    limit.     Read 
Articles  64  and   6&  and  1  ••-.study  article  66- 

Hardness  Testing  Machines 

Hardness  testers  could   not  be  classed  as  testing  machines 
if  the   definition  previously  given  vere   strictly   interpreted.     They 
are   comvaonly  called  testing  machines  and  will,   therefore,  be  dis- 
cussed under  this  heading. 

Filing,   Cutting,   and   scratch  tests  have  been  proposed 
to  test  hardness,   but  the    indentation  method   has  come   into  the  most 
general  use.     The  Brinell  machine  and  the   Scleroscope  represent,-, 
machines  using  the    indentation  method-     Read  Article   61  and   study 
Articles  62  and  $3. 

AUXILIARY  APPLIANCES  BELOVED   IN  LOO) IMG   SPECIMENS 

In  tension  and  compression  tests   it   is  essential  to  have 
the    load   applied  axially  and  uniformly  over  the  cross-section  of  the 
test   specimen. 

Devices  For  Tension  Tests 

Study  Articles  68,   69,   and   read  Article   70.      If  carefully 
used  the   devices    shown  will  give   satisfactory  results.      None   of 
them  give  absolutely  uniform  distribution  of  stress. 

Devices  For  Direct   She?r  Tests 

Study  Article   56  with  Figures   13  and   14  which  are  given 


Civil  Engr-8.  Assignment  2.  Page  10. 

under  testing  machines  in  the  text.  These  devices  give  the  approxi- 
mate shearing  strength  of  the  material  tested/  because  it  is  im- 
possible to  make  the  test  without  producing  some  bending  or  com- 
pressive  stresses  in  the  test  specimen. 

Loading  Appliances  for  Compression  Tests 

Study  Articles  71  to  74  inclusive.  For  ease  in  testing, 
the  spherical-bearing  block  should  be  placed  on  top  of  the  specimen. 
The  radius  of  the  bloc.*,  r   in  Figure  32,  page  76,  should  be  equal 
to  r,  the  radius  of  the  specimen  tested. 

Bedments 

It  is  essential  to  have  flat  surfaces  on  the  ends  of 
compression  test  specimens.   If  possible  the  use  of  bedments  should 
be  avoided.   If  a  flat  surface  cannot  be  secured  plaster  of  Paris 
is  used.  Porous  surfaces  should  be  shellaced  before  being  capped 
with  plaster  of  Paris.  A  satisfactory  surface  can  be  secured  by 
pressing  out  the  excess  p3,aster  on  a  smooth,  plane  surface  of 
glass  or  metal.  The  resulting  bedment  should  not  exceed  1/8"  in 
thickness,  plaster  of  Paris  bedments  should  be  allowed  to  set 
(about  five  hours)  before  testing  the  specimen.   Study  Articles  75 
to  78  inclusive. 

Deformeters 

An  instrument  used  to  measure  the  change  in  length  of 
a  specimen  tested  in  tension  is  called  an  extensometer ;   if  used 
in  a  compression  test,  it  is  called  a  compressoineter.   Any  device 
for  measuring  the  amount  of  bending  of  a  beam  is  a  def lectometer , 
whereas  a  troptometer   is  used  to  measure  the  amount  of  twist  in 
a  torsion  test. 


Civil  Li'.^r-S.  ..3si0nrr.ent   £.  Page   11. 

Extensoraeters :-     Study  the   first  paragraph  aad   those  marked   1,     2 
and   3  of  Article  79,  Article   80  and   the   last  paragraph  of  Article 
82  which  describes  the  Berry  Strain-Gage.     Read  Articlts  81,   83 
and   84.     Note  that  the  Berry  Strain-Gage  could  be  used  as  a  compress- 
ometer.      It   requires  very  careful  manipulation  to  get  accurate   re- 
sults. 

C orupre ssometer  s  ; -     Study  Articles  85  and   36.     The   instrument  shown 
in  Figure   <*6,   page   87,    is  frequently  made  vjith  a  stiff  rod    instead 
of  wires  to  actuate  the  pointer   on  the   dial.      The   rod   is  attached 
to  one   ring  and  bears  on  the  roller   of   a  dial  on  the   other  ring. 
TWO  dials  would  be   required   if  rocs  v,ere  used   in  the  compressomfcter 
shown.     Read  Articles  SI  and   S2.     These  articles  describe   special 
applications   of  compress  outers  and  extensometers. 
Deflectoneters:-       Study  Articles     87  and   90,   read  articles  88 
and   89. 

Troptcmeters :-     Read  Articles  93  and   94. 
Miscellaneous  devices:-     Read  Articles  95  and   97.      Omit     article   96. 


Civil  Er.gr -8.  Questions  to  Assignment  2  Page   12. 

Answer  the  following  questions; 

. 

1.  What   is  a  testing  machine? 

2.  What   is   a  universal  testing  machine? 

3.  Describe  the  mechanism     for  applying  the  load  tosihe 'test- 
specimen  in  a  testing  machine   of  the   screw-gear  type. 

4.  Describe  the  weighing  mechanise  of  a   screw-gear  testing  machine. 

5.  Make  a  diagrarnatic   sketch  of  the  weighing  system  of  a  screw- 
gear  testing  machine 

6.  What  are  the   advantages t   disadvantages,    and   limitations  of 

(a)   screw-gear,      (bj   hydraulic,   and   (c)  Emery  types  of     testing 
machines? 

7.  Describe  the  essential  part   of  the  Er.,ery  testing  machine. 

8.  Name  the  various  types  of  impact  testing  machines. 

9.  What   are  the  advantages  and   disadvantages   of  the  vertical  and 
horizontal  types   of  universal  testing  machines? 

10.  What  are  the   essential  requirements  for      (a)   a  universal  test- 
ing machine          (b)   an  impact  testing  machine? 

11.  Name  the  types   of  hardness  testing  machines. 

12.  Describe  a   scleroscope. 

13.  Briefly  describe  the  various  types  of  endurance   or   repeated- 
stress  testing  machines. 

14.  In  what  units  are   the  test  results  of   (a)   Turner  and    (b)  Rus- 
sell machines  measured? 

15.  What  kind   o5  a  machine  would  you  use  to  determine  the  Shearing 

modulus   of  elasticity  of  a  material? 


Civil  Engr-8.  Questions  to  Assignment  2,  page   13. 

16.  In  what  kind   of  tests  are  spherical   oearihg   blocks  used? 
Why  are  they  used? 

17.  What   is  the  purpose   of  a  bedment? 

18.  Can  the  use   of  bedments  be  avoided? 

19.  Name   the   various  types   of  def oraeters. 

20.  Describe   a  Berry  Strain-Gage. 

21.  What  are  the   advantages  and  disadvantages   of  the  Berry  Strain- 
Gage? 

22.  What   -re  the  essential  requirements  for  extensometers? 
25.     Make  a  diagramatic   sketch  and  describe   a  micrometer* screw 

electric -contact  extensoaeter. 
24.     What   is  a  troptometer? 


JfiUVBKSITY   CF  C*iLIFOKMI«,  EXTENSION  l>  IV  IS  ION 

Correspondence  Courses 
Materials   cf  Engineering  Construction 
Civil  Er.gr -8.  Professor  C.   T.   Wiskocil 

Assignment  3. 

TESTING   OF   STRUCTURAL  lidTER IALS 

Reading  assignment:-        Johnson's  Liiate  rials   of  Construction,   Chapter 
III,   pages  97  to   139. 

preliminary :-     The  foundation  for  a  comprehensive    study   of  the 
Materials  of  Engineering  Construction  will  be  completed  with  this 
assignment.      The   information  is  closely    related  to  the   study  of 
ths  materials  themselves  and  will  possibly  be   found  more    interest- 
ing than  the   first  two  assignments. 

Most   of  the  properties   of  materials  have  been  determined 
by  mechanical  tests.      Materials  whose  properties  are   not  well  known 
rill  be  tested  according  to  present   standards   or  by  methods  to  be 
devised   and  perfected  by  research  testing  which  is  conducted   for 
the   purpose   of  determining  the  proper   size   of  test   specimen,  the 
effect   of  methods   of  procedure   on  the  test  results,   and   similar 
questions. 

The   results   of  mechanical  tests  are   reliable  criteria 
for  the  acceptance    or  the   rejection  of   structural  materials. 
Mechanical  tests  for  quality   and  conformity  to  specifications, 
chemical    analyses,   and  microscopic  examinations  are  used   in  com- 
mercial testing.     Examinations   for  surface  defects,   surface  finish, 
correctness  of  dimensions,   and  the    supervision  of  manufacture  to 
insure  adherence  to  predetermined  methods  are  called    inspection. 


Civil  Bngr-8.  Assignment  3.  Page  2. 

General  observations:-  Study  Article  98.   The  article  emphasizes 
the  fact  that  test  results  are,  in  most  instances,  affected  by  the 
methods  by  which  they  were  obtained.  For  this  reason  it  is  neces- 
sary to  standardize  methods  of  procedure  in  order  that  results  se- 
cured under  such  conditions  may  have  relative  value  at  least.   The 
selection  of  standard  methods  should  be  made  with  reference  to 
the  practical  use  of  the  material.  Materials  anc?  finished  products 
are  tested  under  a  wide  variety  of  standards  which  frequently,  in 
certain  tests,  show  exact  agreement.   Some  of  the  standards  in  com- 
mon use  are:  American  Society  for  Testing  Materials,  Society  of 
Automotive  Engineers,  United  States  Bureau  of  Standards,  United 
States  Navy  Department,  International  Aircraft  Standards,  and  those 
of  Lloyels  of  England. 

Mechanical  tests  classified.--  Study  Article  99.   Static  tests 
yield  most  of  the  published  test  results.  Dynamic  and  wearing  tests 
are  very  important  but  have  not  yet  been  thoroughly  standardized. 
Accelerated  weathering  tests  have  not  proved  satisfactory.  Never- 
theless such  tests  would  supply  very  important  information. 
Structural  tests  are  not  so  v;ell  standardized  as  specimen  tests; 
frequently,  however ,  acceptance  depends  entirely  upon  structural 
tests.   Full-size  forms  are  not  always  tested  to. failure;  anchors, 
for  instance,  are  only  subjected  to  proof-loads. 

THE  ACCURACY  OF  MACHINES  AND  APPARATUS 

Methods  of  determining  the  accuracy  and  sensitiveness  of  testing 
machines:-  Study  Article  100.  Testing  machines  should  be  cali- 
brated when  installed  and  if  the  machine  is  in  constant  use  the  cali- 


Civil  Engr-8.  Assignment  3.  Pag©   3. 

bration  should   be  checked  at  regular   intervals.     The  calibrated 
tension  bar   or  compression  prism  can  be  made   of   such  size  as  to 
load  the  machine  to  be  calibrated  up  to   its  full  capacity.      This 
produces  large  deformation  and    increases  the  relative  accuracy  of 
the  determination.     Furthermore  the  apparatus   is  portable.     This   is 
a  desirable  feature   since  few  owners  of  testing  machines  have  means 
of  calibrating  them  and  must  therefore  call  upon  outside  assistance. 
The  cost   of  such  assistance  would  be  greatly  increased   if  standard 
weights  had  to  be  shipped  for   each  calibration. 

The   so-called    standard  bar  has  a  known  modulus  of  elastici- 
ty  (which  was  obtained   in  a  machine   of  known  accuracy  or   one  whose 
accuracy  was  determined   by  standard  weights).      Its  cross-sectional 
area  and  the   gage   length,    length  over  which  the   deformation  is 
measured,  are  also  known.     The  actual    load  producing  any  measured 
deformation  can  be   readily  computed. 

This  computed   load   is  then  compared  with  the   load   observed 
on  the   scale-beam    of  the  machine.     The  difference   between  the   loads, 
divided  by  the   actual  or  true   load   is  the  percentage  error    in  the 
machine.      Its   sign,    indicating  whether  the  machine   reads  high  or 
low,    should  always  be   given.      In  a  well-designed  machine  the  per- 
centage error   is     constant   over   its  entire   range.     The   extensometer 
must  be  permanently  attached  to  the   standard  bar. 
The  calibration  of  apparatus  for  measuring  deformations;-     Read 
Article   101.      It   is  not  necessary  that  measuring  apparatus  be  cor- 
rect.     The  errors,   however,   must  be  known  and  they  should  pre- 


Civil  Engr-8.  Assignment  3.  Page  4. 

ferably  be  constant  or  should  change  at  a  constant  rate.  For  any 
important  test  or  investigation  all  apparatus,  including  machines 
and  instruments,  should  be  calibrated.  If  in  error,  the  required 
corrections  must  be  applied  to  the  observed  measurements. 

SELECTION  AND  PREPARATION  OF  SPECIMENS 

Selection  of  specimens;-    Study  Article  102.  The  proper  selec- 
tion of  samples  is  of  great  importance.  Careless  or  improper 
sampling  is  one  of  the  most  serious  sources  of  trouble  in  commercial 
testing. 

The  preparation  of  the  specimen:-  Study  Article  103.   It  has  been 
known  for  a  long  time  that  the  size,  s;hape  and  method  of  preparation 
of  the  test  specimen  affect  the  test  results.  The  effect  of  these 
controlable  variables  is  studied  in  research  testing  which  is  be- 
ing carried  on  in  government,  industrial,  and  educational  labora- 
tories. 

XENSION  TESTS 

Tension  tests  are  universally  used  to  specify  the  proper- 
ties of  ductile  materials.   They  are  so  generally  used  because  they 
give  the  elastic  limit  strength,  ductility,  and  toughness  besides 
the  tensile  strength  and  modulus  of  elasticity.  When  the  strength 
of  a  material  is  spoken  of  it  is  generally  understood  to  mean  the 
maximum  tensile  strength.   The -best  practice  is,  however,  to 
specify  the  particular  strength  meant.  Brittle  matter ia Is,  namely 
cast  iron  and  cementing  materials,  are  tested  in  tension. 

Only  the  ultimate  tensile  strength  of  these  materials 


Civil  Engr-8-  Assignment  3.  Page  5. 

is  obtained.  Cements  are  tested  in  tension,  because  the  machine 
for  such  tests  is  much  cheaper  than  a  compression  machine  and  the 
specimens  are  more  easily  prepared  and  tested.   Tension  tests  are 
gradually  giving  wa^  to  the  compression  test,  because  cement  and 
mortar,  which  are  brittle  materials,  are  generally  used  in  com- 
pression. 

Study  Articles  104,  105,  the  first  and  last  paragraphs 
and  the  tsxt  under  Figure  2  on  page  106  in  Article  106, 

Read  ^j-ticle  107.  The  essential  points  to  remember  are: 
The  averagb  diameter  or  dimensions  are  determined  and  the  gage 
length  then  laid  off  (usually  2"  or  8";^  The  gage  length  is  not 
divided  into  equal  spaces  as  indicated  in  the  text.  The  speed  of 
testing  should  be  such  that  the  scale-beam  can  be  kept  in  balance 
so  chat  the  phenomena  of  yield  point  and  maximum  can  be  accurately 
determined.  The  properties  of  soft  steel  do  not  seem  to  be  effected 
by  speeds  up  to  six  inches  per  minute. 

Study  Article  108,  109,  110  and  111.   See  the  typical 
stress-deformation  curves  on  pages  210,  256,  476  and  601.  The 
drop  of  the  scale-beam  indicates  the  yield  point  in  the  commercial 
tension  test  of  medium  carbon  steel  or  any  material  having  a  de- 
cided yield  point.  The  load  is  applied  continuously  and  the  scale- 
beam  is  kept  balanced.   In  order  to  keep  the  beam  in  balance  the 
poise  -weight  must  be  advanced  at  a  steady  uniform  rate,  depending 
upon  the  speed  at  which  the  cross-head  of  the  machine  is  moving. 
At  the  yield  point  the  rate  of  increase  in  load  is  suddenly  changed 


Civil  Fngr-8.  assignment  3.  Page  6. 

and   in  sane  cases  actually  becomes  negative    (see  Figure  2  page  811, 
diagrams  for  G.37f0  and   0.53$  oar  boa  steels).      Before  the   rate   of 
motion  of  the  poise-weight  can   be  changed   it  has  advanced  too  far 
and  causes  the  beam  to  fall,    sometimes  the   load  actually  decreases 
as   in  Figure  2   just  referred  to,   so  that  the  beam  is   out   of  balance. 
This  phenomenon  is  known  as  the   drop  JD£  beam. 

COMPRESSION  TESTS 

The   compression  test   is  used  chiefly  for  the   brittle 
materials.      Study  Article   112.     Read  Article   113,    study  Figure  7 
on  page   114   in  this  article.     Whereas  the  compression  test  specimens 
in  the   past  have  been  cubes,   the  tendency  is  to   increase  the    length 
of  the   specimen.     Most  concrete   specimens  are  6"  in  diameter  and 
12"   long..     Mortar   specimens  are  2"   in  diameter  and  4"   long  while 
met^l  specimens  %re  aoout   1"   in  diameter  and  4U   long.      Omit  Article 
114. 

Tne   important  facts  in  Article   115  are:     that  when  the 
elastic    limit  and  modulus  of  elasticity  are  determined  the  defor- 
mation should  be  measured   on  at   least  two  sides  and  the  yokes   of 
the   compressometer   should   be  placed  not   less  than  half  of  the 
diameter   from  the   nearest  bearing  surface.     A  spherical  bearing 
plate   should  be  used. 

Study  Articles   116   and    117. 

TRANSVERSE   TESTS 

Study  Articles   118  to  122   inclusive,    omit   only  Table   1, 
page   122.      The  calculated   stresses   of  tension  and  compression  - 
modulus   of  rupture   -  are  nominal  values  and   are  higher  than  the 


Civil  Engr-8.  Assignment  3.  Page  7. 

actual  stresses.     Cast   iron  is  the   only  material  in  which  the  size 
of  the  test  piece  affects  the  modulus  of  rupture.      In  other  materi- 
als  it  is   independent   of  the   size   of  the  specimen,  provided, of 
course,   that  the  material  is  the   same,  but  depends  upon  the   shape 
of  the  cross-section. 

IMPACT  TESTS 

Study  Articles   123  to  127   inclusive.      No  impact  test  has 
"been  accepted  as  a  universal  standard  because  the  results  are 
affected  by  both  the   design  of  the  machine   and  the   shape  and  size 
of  the  test   specimen.     A  drop-test  for  railway  rails  has  been 
standardized   and  adopted,   see  Figure   20, page  67.          Lloyds  Register 
of  Shipping  specifies  a  definite  drop-test  for  ship  anchors.     The 
notched-bar  test   of  the  Charpy  and  similar  pendulum  machines   is 
quite  widely  used   in  Europe  but  has  not  been  adopted  here. 

HARDNESS  TESTS 

Study  Articles   128  to  135  inclusive;      Omit  Taole  2     on 
page   129  and  the  formulas  in  Article   134.     The  Brinnell  machine 
and  the  Scleroscope  both  test  the  relative  hardness  or  the  uni- 
formity  in  hardness  of  a  given  material.      The  Scleroscope   is  well 
adapted  to  testing  the  hardness  of  gear  teeth.      When  a  manufactured 
piece  has  given  satisfactory  service,    its  hardness  may  be  determin- 
ed;  and   other. pieces  bought   later  may  be   required  to  show  the   same 
degree   of  hardness.      Hardness  depends  upon  other  properties  and 
for   any  given  material  the   hardness   indirectly  measures  the  tensile 
strength. 


Civil  Er.gr-8.  Assignment  3.  Page  8. 

Study  Articles  136  to  139  inclusive.  Remember  that  the 
direct  shear  test  will  determine  only  the  breaking  strength  in 
shear. 

TORSION  TESTS 

Study  Articles  140  to  142  inclusive.  Remember  that  the 
torsional  modulus  of  rupture,  the  ultimate  shearing  stress  in  tor- 
sion computed  from  formula  16  on  page  22,  is  not  the  actual  shear- 
ing strength  of  the  material.  The  formula  is  similar  to  the  one 
for  extreme  fiber  stress  in  bending,  the  modulus  of  rupture.  Ten- 
sion is  a  secondary  stress  developed  in  the  torsion  test;  for 
brittle  materials  it  is  less  than  the  shearing  strength  and  brittle 
materials  subjected  to  torsion  will,  therefore,  fail  in  tension. 
The  torsion  test  will,  however,  determine  the  modulus  of  rigidity 
of  brittle  materials. 

BEND  TEST  OF  METALS 

Study  Articles  143  to  148  inclusive.   The  bend  test  is 
generally  used  to  estimate  the  ductility  of  metals,  the  metal  may 
be  cold  or  heated.  The  test  can  be  used  to  determine  whether  a 
given  metal  is  ductile  enough  to  be  put  through  certain  manu- 
facturing processes. 

DRIFTING  TEST  OF  METALS 

The  drift  test  like  the  bend  test  gives  an  indication  of 
the  ductility  of  metals.   It  is  used  on  steel  plates  to  be  fastened 
together  by  rivets  because  rivet  holes  in  field  joints  are  brought 
into  alignment  by  the  use  of  a  drift  pin.   This  operation  should 


Civil  F-ngr-3.  Assignment  3.  Page   9. 

not  cause  the  metal  to  crack  or  tear.      In  the  best  grade   of  wori£ 
rivet   holes  should   be   reamed,   because   drifting  weakens  the   joint. 
Study  Article    149. 

RESUME   OF  CHAPTER    III 

Study  Article  150;  it  is  a  condensed  statement  of  the 
properties  revealed  by  the  testa  described  in  the  assignment  and 
the  uses  made  of  the  tests. 


Civil  Engr-8        Questions  to  Assignment  3.          Page  10. 


Answer  the  following  questions;* 

1.  What  should  be  the  guiding. principle  in  the  preparation  of 
new  testing  methods  and  the  design  of  testing  machines? 

2.  Make  a  list  of  structural  forms,  machines  or  machine  parts 
which  are  tested  as  a  v/hole  or  full-size. 

3.  Name  the  different  ways  of  calibrating  testing  machines. 

4.  Describe  the  standard  bar  method  of  calibrating  a  testing 
machine. 

5.  In  the  method  described  in  question  4  make  a  sample  calcula- 
tion to  show  how  the  error  and  the  percentage  error  in  a 
testing  machine  is  calculated.  Assume  all  necessary  data. 

6.  What  are  the  objects  to  be  kept  in  view  when  selecting  samples 
for  test  specimens? 

7.  What  are  the  general  requirements  for  the  preparation  of  test 
specimens? 

8.  What  is  the  significance  of  the  tension  test? 

9.  What  is  a  commercial  tension  test? 

10.  Describe  the  tensile  fracture  of  medium  carbon  steel. 

11.  How  is  the  yield  point  in  a  tension  test  determined? 

12.  What  causes  the  drop  of  beam  in  the  tension  test  of  medium 
carbon  steel? 

13.  How  is  the  elongation  in  a  tension  specimen  distributed  with 
reference  to  the  point  of  fracture? 

14.  Prepare  a  stress-deformation  diagram.  Put  in  a  curve  for 
mild  steel  and  show  the  elastic  limit,  the  apparent  elastic 
limit,  the  proportional  limit  and  the  yield  point. 

15.  Make  a  list  of  materials  usually  tested  in  tension. 

16.  What  information  can  be  secured  from  a  compression  test? 

17.  Make  a  list  of  materials  usually  tested  in  compression. 

18.  How  are  the  deformations  in  the  transverse  test  measured? 

19.  What  materials  are  tested  in  bending? 


Civil  Er.gr-8.       Questions  to  Assignment  3.        Page  11. 


20.  What  is  the  object  of  the  impact  test? 

21.  Compare  the  Brinnell  and  Scleroscope  methods  for  measuring 
hardness. 

22.  How  does  direct  shearing  stress  differ  from  the  shearing 
stress  computed  in  the  torsion  test? 

23.  What  information  can  be  obtained  in  the  torsion  test? 

24.  How  do  brittle  materials  fail  in  torsion? 

25.  What  property  of  materials  is  determined  in  the  bend  test? 

26.  Name  materials  which  are  tested  in  bending. 


UNIVERSITY  OF  CALIFORNIA.  EXTENSION  DIVISION 

Correspondence   Courses 
Materials   of  Engineering  Construction 
C'.vil  Engr-8.  Professor   C.    T.   Wiskocil 

Assignment  4. 

USES  AND  PHYSICAL  PROPERTIES  OF  WOOD 

Reading  Assignment:-     Johnson's  Materials   of  Construction,  Chapter 
IV,     pages   140  -   178. 

Introduction;-     Wood   is  one   of  the  primary  materials   of  construction 
and,   due  to  the  ease  with  which  it  can  be  worked  and   its  comparative 
light  weight,    it  has  always  been  used  as  a  structural  material. 
Wood  has  sufficient   strength  and  hardness  for  general  purpose s^but   .. 
is   inflammable  and   subject  to  decay.      Its  general  use   is  therefore, 
confined   to  inexpensive   or  temporary  construction.      It   is  used  for 
railroad  ties  chiefly  because   of  its  resilience. 

Wood    is  an  organic  material.      Its  physical  and  mechanical 
properties  are   dependent  upon  its   structure,  which   in  turn  is  de- 
pendent upon   life  processes,   age,   and   other  physiological  causes. 
Because    of   its   complex  cellular    structure    specimens   of  wood  cut  from 
the   same   stick  and  appearing  to  be   identical     often  show  marked 
variations   in  strength. 

Importance   of  Wood:-         Read  Article   151.      The   latest  estimates   in- 
dicate that  there    is  a  total  of  2,800  billion  board   feet   of  standing 
timber   in  the  United   States.    (Timber   is  usually  measured   in  board 
feet.      The  unit   is   one  foot    square  and   one   inch  thick  or   144  cubic 
inches).      This  estimate    includes   only  trees   of   sawlog  size  and   aot 
wood  that  could  be  used  for   such  purposes  as  fuel  and   pulp. 


Civil  Engr-8.  Assignment  4.  page  2. 

It  has  been  frequently  stated  that  the  -supply  of  timber  in 
the  United  States  will  be  exhausted  within  the  next  thirty  or 
forty  years  because  the  rate  of  annual  depletion  by  insects,  fires, 
and  lumbering  (wood  cut  for  all  purposes)  is  aoout  100  billion 
board  feet.   Remember  that  these  are  scientific  estimates  and  the 
extent  to  which  known  factors  will  control  the  result  cannot  be 
exactly  determined  and  the  possibility  of  unknown  factors  must  be 
provided  for.   The  virgin  forests  of  Douglas  fir  and  southern 
yellow  pine  alone,  will  continue  to  supply  satisfactory  structural 
timber  for  several  generations.   The  increasing  practice  of  forestry 
will  insure  an  increased  annual  growth  and  minimize  the  occurrence 
of  fires.   Three  California  redwood  companies  have  announced  plans 
for  permanent  forest  management  whereby  they  will  work  their  prop- 
erties so  as  to  yield  regular  crops  of  timber  and  thus  insure  a 
permanent  supply  of  raw  material  for  their  plants.   Large  tracts 
of  non-agricultural  land  which  are  well  suited  for  the  production 
of  timber  could  be  utilized  if  necessary.   Furthermore  the  more 
general  use  of  preservatives  and  the  more  economical  use  of  wood 
both  tend  to  conserve  the  supply.   The  exhaustion  of  our  forests  is, 
therefore,  problematic. 

Production:-  About  one  half  the  available  supply  of  timber  in  the 
United  states  is  in  the  Pacific  Coast  forests  (Washington,  Oregon, 
California,  Idaho,  and  Montana).   It  consists  principally  of 
Douglas  fir,  western  hemlock,  sugar  pine,  western  yellow  pine, 
redwood,  and  cedar. 


Civil  Engr-8.  Assignment  4.  page  3. 

The  annual  production  of  timber  is  about  forty  billion 
board  feet.  Washington  and  Louisiana  produce  the  most;  together  they 
supply  about  one  fifth  of  the  total  production. 

About  one  fifth  of  the  wood  cut  annually  is  used  in  engineer- 
ing construction.   The  following  table  gives  the  approximate  dis- 
tribution: 

Structural  timber  and  lumber  13  % 

Ties  4 

Mine  timbers  2 

Car  construction  1 
Poles  .2 

Ship  construction  .2 

About  40  %  is  used  for  firewood  and  \Z%  for  pianing-miil  products 
such  as  doors  and  window-sashes.  Wood  is  also  made  into  pulp, 
shingles,  laths,  furniture,  posts  and  containers  (barrels,  boxes, 
and  crates). 

Wood,  Timber,  and  Lumber:-   Wood  is  the  hard  fibrous  substance  of 
trees  and  shrubs.   It  is  composed  of  lignocellulose ,  which  is  a 
starch- like  substance,  permeated  by  materials  known  as  lignin, 
resin,  coloring-matter,  water  and  small  proportion  of  inorganic 
matter  (evident  as  ash). 

Timber  is  wood  suitable  for  construction  whether  in  the 
tree  or  cut  and  seasoned.  When  applied  to  cut  wood  the  term  is 
used  to  designate  pieces  of  comparatively  large  breadth  and  width. 

Lumber  is  timber  that  is  sawed  or  split  into  boards,  planks, 
or  other  forms  of  comparatively  small  dimensions.   This  term  is 
used  chiefly  in  the  United  States. 


Civil  Fngr-8  Assignment  4. 

GENERAL.  CHARACTERISTICS  OF  WOOD 

Structure  and  appearance : -Read  Article  152.  A  knowledge  of  the 
structure  of  wood  is  important  because  of  its  relation  to  the  mechani- 
cal properties.   In  general  the  structure  is  cellular,  consisting  of 
minute,  hollow,  elongated  tubes  grown  together  and  closed  at  the 
ends.   In  some  woods  the  tubes  are  open  to  permit  the  movement  of 
sap.  Because  of  its  structure  and  composition  wood  can  "be  cut 
easily  and  nails  and  other  fastenings  can  be  readily  driven  into  it. 
The  empty  cells  are  dead  air  spaces  and  retard  the  conduction  of 
heat  and  sound.  Because  of  its  porous  nature  it  will  take  up  pre- 
servatives. Paint  and  ether  surface  finishes  will  readily  adhere 
to  its  surface  and  thus  prolong  its  life. 

Classes  of  trees:-  Read  Article  153.  The  botanical  classification 
of  trees  whose  wocd  is  used  in  construction  in  the  United  States  is 
as  follows  : 

I   Gymno sperms 

I  A  Coniferae 


II  Angiosperms 

IIA     Dicotyledons 

The   seeds   of  the   gymnospermB  are  not  enclosed    in  fruit.      The  gymno- 
sperms  are   divided    into  three   groups.      TWO  of  them  grow  principally 
in  the  tropics;   tne   other   one,   the  coniferae,    is  the   only   one  that 
yields  merchantable    lumber.      The  pines,    firs  and  cedars  are   some 
of  the  trees   included    in  this  group.      The   seeds  are   borne   on  a 
series  of  overlapping   scales,   arranged   on  cones.      The   leaves  are 
narrow,   stiff  or   needle-like.        The  trees  are   sometimes  designated 


Civil  Engr-8.  Assignment  4.  page  5. 

as  needle-leaf,    softwood,   evergreen,  coniferous,  and   cone-bearing. 

The   seeds  of  the  angiosperms  are  always  enclosed.     There  are 
two  groups   of  angiosperms.     They  differ  principally  in  the   structure 
of  their   stems   or  trunks.      The  first  group,  the  monocotyledons, 
have   one   seed   leaf  or  cotyledon  (therefore  the  name  mono-cotyledon;. 
These  trees,  which  include  the  palm  and  the  bamboo,   grow  principally 
iu  the  tropics.     The    second  group,  the  dicotyledons,   have  two  seed- 
leaves.     This  group  includes  the   oaks,  maples,   and   hickories,  which 
are  sometimes  called   broad-leaf,   hardwood,   or  deciduous  trees. 

The  conifers  yield  the   largest  proportion  of  woods  used  for 
structural  purposes. 

Classification  of  Woods;-       Frequently  woods   instead   of  trees  are 
classified.      In  the  botanical  classification  of  trees  given  in  a 
previous  paragraph  the  two  important  groups  were  the  conifers  and 
the  dicotyledons.     They  grow  in  the   same  manner  and  their  woods, 
therefore,   are   in  one  group  sometimes  called     out side -growers, 
banded  woods,   or  exogens.     The   elements  of  the  woods   in  this  group 
develop  in  the  cambium  layer  which  is  just   inside  the  bark  of  the 
tree.     Each  growing  season  new  wood   is  added  to  the  previous  growth. 
In  cross-section,  these   seasonal  additions  appear  as  concentric 
circular   layers   or  rings.      The  names  conifers  and   dicotyledons  are 
applied  to  the  divisions  of  this  group.      The  designation  soft-wood 
for  the  conifers   is  not   logical  because    some   of  the  woods  of  this 
division  are  actually  very   hard  as   in  the  case   of  some   of  the  pines, 
while  the  term  hardwood    is   incorrectly  applied  to  the  dicotyledons 


Civil  Engr-8.  Assignment  4.  page  6. 

basswood  and  chestnut  whose  wood   is   soft.      The  terms  needle-leaf 
and   broad-leaf  are  more   exact  but  the  designation  conifers  and 
dicotyledons   is  preferable. 

The   other  group  of  woods   includes  the  unimportant  mono- 
cotyledons  in  which  the  wood  elements  are   in  separate  bundles  scat- 
tered throughout  the  tree.     The  cross-section  of  these  woods  has 
a  dotted  appearance.     The  trees  grow  largely  by  expansion  of  the 
cells  already  formed  and  do  not  continually  increase   in  diameter 
but  attain  their  maximum  diameter  early  in  their  growth.     The  name 
endogen     is  sometimes  given  to  this  group;   other  names  are   inside- 
grower  and  non-banded  woods.     The  use   of  the  terms  endogen  and  exo- 
gen  should  be  avoided  because  engineers  and  botanists   seldom  em- 
ploy them  in  the   same  way. 

Botanical  Names:-     The  use   of  botanical  nomenclature   obviates  the 
confusion  v,'hich  occurs  when  trees  are  designated  by  common  or   local 
names.     Thus  the   names  of  the   species  Pinus  palustris  are   longleaf, 
yellow,   hard,  Georgia,  and  southern  pine,    in  addition  to  some  25 
others. 

Botanical  names  are  made  up  of  terms  which  denote  genus  and 
species.  Sequoia  is  the  generic  name  for  all  species  of  redwoods. 
Sempervirens  and  washingtoniana  are  names  of  particular  species  of 
redwoods;  the  latter  is  the  Big  Tree  or  Mammoth  Redwood. 

Botanists  have   sometimes  given  different  names  to  the   same 
species*      The  abbreviated   name   of  the  person  responsible   for  a  given 
designation  is  therefore  added  to  the  complete  name.     An  example 
is  Sequoia   sempervirens  Endl. 


Civil  Engr-3.  Assignment   4.  page   7. 

A  genus   is  a  group  of  related   species  while  a  species   is  the 
smallest  group  of  individuals  to  which  distinctive  characteristics 
can  "be  assigned. 

Structure   of  wood   in  general:-       Read  Article   154.     The  accompanying 
diagram  shows  the  cross-section  of  a  tree.     The  pith  stores  up  plant 
food   for  the  young  stem  and    it  seems  to  be   of  only  temporary   service. 
A  layer   of  spring  wood  and   one   of   summer  wood   constitute  a   so-called 
annual  ring.     Early  and   late  growth  would   be  better  designations  for 
the   parts   of  the  annual  rings.     Early  growth  is  usually  formed   in 
the   spring  when  the  tree   requires  most  water.     The  water-conducting 
wood -elements  predominate   and  produce   porous   or   less  compact  wood. 
The   late   growth   is  formed   in  the   summer  and  early  fall;   it   is 
heavier  and  denser  than  the  early  growth.     Distinct  periods   of  rapid 
and    slow  growth  may  be  caused  by  wet  and   dry   seasons  which  sometimes 
occur   oftener  than  once  a  year.     The  number   of  so-called  annual 

rings  does  not  always  give  the   exact  age   of  the  tree.     This  has  been 

at 
found  to  be   the   case   in  certain  trees  which  were  c:ut/a  known  age. 


Pith 
Cambium^          _J  Heart  \\ ood 

3ar.<    ^  ,,  ,  ^  „- 

Wood 


_ Spring  Wood   (light) 
-SuiEraer  Wood     $ark 


Cross  Section  of  Tree 


Civil  Engr-8  Assignment  4.  page  8- 

HBARTWOOD;-  While  the  ceil  structure  of  heart-wood  is  the  same  as 
that  of  sapwood,  the  protoplasm  is  absent  and  inert  minerals  and 
pigments  appear.   The  thicker  cell-walls  of  heartwood  are  probably 
caused  by  the  accumulation  of  deposited  materials.   The  change  from 
sapwood  to  heartv/ood  does  not  take  place  ring  by  ring  or  a  little 
each  year  but  may  skip  many  years  and  eight  or  more  rings  may  change 
to  heartwood  in  one  year.  The  change  is  not  uniform  around  the  tree, 
it  may  occur  in  one  side  before  the  other  so  that  one  ring  may  be 
part  heartwood  while,  the  other  part  remains  sapwood.  (Reference  - 
U.S.  Bureau  of  Plant  industry  Bulletin  No.  14  p.  15.;   In  most  trees, 
however,  the  line  of  division  between  the  heartwood  and  the  sapwood 
and  that  between  the  sapwood  and  the  bark,  are  concentric  around  the 

pith.  , 

S^PWOOD :-     Sapwood    lies  between  the   bark  and  the   heartwood.      It  de- 
rives  its  name   from  the  fact  that   it  carries  up-ward   sap  currents. 
(The   descending  currents  pass  through     the   inner   bark) 
BARK:-     The  barK  affords  protection  to  the  tree  and    is  an  agent   in 
its  development. 

CAMBIUM  LAYER:-     The   cambium   layer   consists   of  a  thin   layer    of   small 
cells  between  the   bark  and   the   sapwood.      These   cells  develop   into  the 
wood   cells   of  the  sapwood   and   form  the  annual  rings.      The   outer 
cambium  cells  develop   into  new  bark. 

GRAIN  OF  WOOD:-     Study  Article    155.     Wood   is   said  to  be   straight 
grained  when  the   direction  of  the  wood   elements   is  parallel  with  the 
pith-      If  the  elements  are   arranged   in  a  spiral  course  around  the 


Civil  Engr-8.  Assignment  4.  Page  9. 

pith,   the  wood    is   spiral  grained.     The  grain  of  a   small  stick  is 
influenced   by  the  way   it   is  cut  from  the    log.      If  the   lines   on  the 
surface    (formed   by  cutting  the   annual   layers   of  v;ood   cells)   run 
diagonally  across  the  piece,   the   bending  and   compress ire   strength 
will  be   reduced.      Iriclination  of  more  than  1   in  20  to  the  edge   of 
the   stick  should  not  be  allowed   in  high  grade  material.     Spiral 
grain  can  be   detected  by  season  checks  or  by  splitting  the   stick. 
STRUCTUHAL  ELEMENTS  OF  WOOD:-     Study  Article   197.      The   four  princi- 
pal wood  elements  are  tracheids,  wood   fibers,   vessels,  and  parenchyma, 
The  cell  walls  of  these  elements  are  composed   of  Xylem  (xl/  -  lem) 
or  wood  tissue. 

Tracheids  are  small  thin-walled  tubular  cells  which,    in 
coniferous  wood,  are  about  0.2   inches   long  and  polygonal  in  cross- 
section  with  a  diameter   of  aoout  0.002   inches,     The  cells  with 
their    longitudinal  axis  parallel  with  the   pith  of  the  tree,  are 
arranged    in  radial  rov;s.      The  thick  walls  of  the   cells  formed  to- 
ward the   end   of  the   season's  growth  reduce  the   size   of  the   opening 
in  the   cells  but  add  to  the   strength  of  the  element.      Tracheids 
have   bordered   pits   in  their   side  v;alls.      These   pits  are   small  por- 
tions  of  the  wall  where   the   original  cellulose  membrane   of     the 
cambia 1  cell  has  not  been  thickened   by  the  addition  of  lignin 
(inert  minerals).      These  pits  allow  the  passage   of  water  between 

adjacent  cells. 

Wood  fibers  are   small  thick-walled  tubular  cells  with  taper- 
ed ends   rarely   over  0.1   inch   in  length.      They  usually  have   small 


Civil  F.ngr-3.  Assignment  4.  page    10. 

simple   pits.      They  are  not   found    in  coniferous -woods,   but  are  -che 
principal  source   of  hardness  and  toughness  of  broad    leaved  woods. 

Vessels  are   long  tubular  elements  with  mfcny  border  pits. 
Vessels  often  extend  the   entire   length  of  the  tree.      The;,   vary  in 
diameter  from  0.003  to  0.03   inches.     They  are   formed  by  the  union 
of  original  cambial  cells   in  which  the  end  walls  become  partially 
or  wholly  absorbed   so  that  they  present  an  unobstructed  passage  for 
water   from  the   roots  to  the  branches  of  the  tree. 

Parenchyma  are  made   of  thin-walled  cells  joined  end  to  end. 
The  end  and  side  walls  are   of  equal  thickness  and  have  many  simple 
rounded  pits.     Parenchyma  resemble  wood  fibers  in  shape.     Their 
chief  function   is  the   storage  and   distrioution  of  food  materials. 

Pays,   often  called  medullary  rays,   are   radial  bands   of  cells 
which  cross  the  tree  at   right  angles  to  the  pith.      In  some   species 
the   rays  are  composed   of  parenchyma,    in  others,  the  cells  are   tracheids 
The   principal  function  of  the   rays   is  the   lateral  distribution  of 
plant  food. 

Coniferous  woods  are   composed  principally  of  tracheids  with 
rays  at   right  angles  to  these  cells.     Resin  ducts   occur   in  the  resin- 
bearing  trees  usually  between  the   early  and  the   late  wood.      These 
ducts  have  no  walls   of  their   own  but  are   only   intercellular  channels 
with  an  average  diameter   of  0.01  inches  for  the   larger  ducts.     Coni- 
ferous woods  are  quite  uniform  in  cross -section  and  because   of  the 
absence   of  large  vessels  are  called  non-porous.      The  thick-walled 
cells   in  the    late  wood  give  that  portion  of  each  annual   ring  a 
darker   color  than  the   early  wood.      Study  Article    198. 


Civil  Engr-8.  Assignment  4.  page   11. 

Broad  leaved  woods  have  a  more  complex  structure.     They  con- 
sist chiefly  of  wood  fibers  with  prominent  medullary  or  pith  rays 
of  parenchyma.     Broad    leaved  woods  are   ring-porous  or  diffuse- 
porous  depending  upon  the  distribution  of  vessels  or  pores.      In 
the   ring-porous  woods  the   pores  are   grouped   in  the   early  wood  and 
make  a  pronounced  annual  ring,     whereas  in  the  diffuse-porous  woods, 
the  vessels  have  a  uniform  dispersion  and  the  annual  rings  are  not 
so  distinct.      Stuoy  Article    199,   note  the   statement   regarding  tyloses 
£See  Figure   2   on  page   143).      Omit  Article   200. 

DEFECTS   IN  TIMBER:-     Study  Article   156.      The  most  common  defects   in 
timber  are  knots,  checks,   and  shakes.     Knc*s  are  classified  as  sound, 
loose,   or  decayed.     They  affect  the  compressive  and  transverse 
strength  of  wood,  also  its  workability  and   shrinkage.     Checks  are 
caused  by  stresses  set  up   in  seasoning.      Large  structural  timbers 
are  difficult  to  season  without  checking.     The   outer  portions  dry 
and    shrink  while  the   inner  part   is   still  tooist,  thus  bausing  the 
wood  to  split. 

A  shake   is  a  separation  between  two  annual  rings. 

Both  checks  and   shakes  decrease  the   resistance  to  longitudinal 
shear  besides  affecting  the  durability  by  admitting  air   and  moisture* 
poles  with  checks  the   entire   length  are  also  weak  in  torsion  -  the 
cross-arms  twist  the  pole  when  the  wires  break. 

Density  and  weight;-       Study  Article   158.      The  term  specific  weight 
means  the  weight   of  a  specific   or  definite  volume,   which  in  this 
book  is  taken  as  the   cubic   foot.      The   specific  weight   of  different 


Civil  Engr-3.  Assignment  4.  .Vage  12. 

woods  varies  with  the  moisture  Content.  With  a  given  percentage 
of  moisture,  however,  the  specific  weights  for  each  species  are  not 
the  same  hut  they  vary  due  to  the  structure  of  the  •wood.   The  amount 
of  wood  substance,  then,  determines  the  specific  weight.  Wood  sub- 
stance itself  with  a  specific  gravity  of  1.55  would  not  float  on 
w&ter.  A  cubic  foot  of  water  weighs  62.5  pounds,  a  cubic  foot  of 
wood  substance  (not  possible  in  natures)  would  weigh  1.55  times 
62.5  or  approximately  97  pounds.   (A  cubic  foot  of  anthracite  coal 
weighs  about  97  pounds,  j  The  following  table  indicates  the  effect 
of  moisture  on  the  specific  weight  of  the  species  of  wood  listed. 
Air -dry  wood  contains  from  12  to  15  %  moisture  while  a  wood  with 
Q%  moisture  is  said  to  be  kiln  dry.  Note  that  the  average  specific 
weight  for  a  given  lot  of  wood  may  vary  by  ±  5  %  from  the  values 
in  the  table  and  individual  pieces  may  show  as  auch  as   -  20  % 

variation.  Air'   Kiln- 

Green  Dry    Dry 

Blue  gum  (Eucalyptus  globulus;  70  54  52 

White  oak  (Quercus  alba)  61  47  46 
Douglas  fir  (Pseudotsuga 

taxifolia;  40  33  32 
?fe stern  yellov,  pine  (Pinus 

ponoerosa,  53  29  28 

Sugar  pine  (pinus  lambertiana)  50  27  26 

Sitka  spruce  (Ficea  sitchensis)  33  26  25 

Redwood  (Sequoia  sempervirens)  38  24  23 

Western  red  cedar  (Thuja  plicata)  24  22  21 

Moisture  in  wood ;-  Study  Article  159.  Water  exists  in  only  two 
conditions  in  wood,  -  (1)  as  free  water  in  the  pores  and   (2)  as 
absorbed  water  in  the  cell  walls.   (1)  and  (2)  as  given  in  the 
text  are  practically  identical.   The  moisture  content  of  green  wood 
as  given  in  Table  I,  facing  page  196,  is  computed  on  the  basis  of 


Civil  Eiigr-8.  Assignment  4.  page  13. 


cried  to  a  constant  weight  at  luO  degrees  Centigrade. 
The  crying  of  tinker:-  Study  Article  160.   The  principal  reasons 
for  ,se-uscn.tn£  v.ood  are  given  in  the  first  part  if  Arti:;l<?  160.  Most 
wood  is  se?  p.oneo  in  the  open  air,  Under  these  conditions  the  rata 
of  drying  varies  v/ith  the  temperature  and  humidity  of  the  air,  size 
and!  species  of  wocd  and  method  of  piling.   Sawed  lumoer  is  piled 
so  as  to  permit  the  free  circulation  of  air.   In  piling  wood  for 
air  -seasoning  care  must  be  taken  to  have  good  foundations  for  the 
stacks,  rrhich  wust  be  Kept  free  from  debris  and  the  yards  should  be 
well  drained.  Air  seasoning  usually  takes  considerable  time  a§ 
ixidicated  in  Figure  6  on  page  151.  Defects  produced  by  improper 
drying,  have  sorbet  imes  caused  losses  of  25^  of  the  seasoned  -wood. 

Hi  In  drying  is  re-sorted  to  "when  ^cod  must  be  seasoned  quickly. 
A  recent  development  of  a  kiln-drying  process  which  makes  use  of 
superheated  stea-ri  has  been  announced  by  the  U.S.  Forest  products 
Laboratory.   C-rean  coniferous  lumber  (such  as  Douglas  Fir  and 
Southern  Yellow  P:'ne)  one  inch  thick  can  be  dried  to  10  %  moisture 
content  in  14  hours  by  this  method.   It  is  not  recommenced  for 
lumber  over  2  irshes  thick, 

In  the  rap'.o  .seasoning  of  \<cou  care  must  be  taken  to  prevent 
the  evaporation  o.C  water  fVcm  the  surface  at  a  faster  rate  than 
ic  is  brought  from  the  interior  of  the  -?ood.   The  surface  evaporation 
can  be  controlled  in  a  ^vell  designed  kiln  by  regulating  the  humidity, 
temperature  and  amount  of  air  passiag.  through  the  kiln.   Evaporation 
in  a  kiln  depends  upon  the  relative  humidity  of  the  air.  Air  -with 
a  relative  humidity  of  100  ^.cannot  dry  7/ood  because  it  already 


Civil  Lngi'-S.  Assignment  4.  Page  14. 

contains  ail  the  water  it  can  carry,  but  if  the  relative  humidity 
is  .'educed  to  say  60  %  it  can  taice  up  a  certain  amount  of  moisture. 
A  large  amount  of  air  is  required  in  the  successful  operation  of 
a  kiln.   Typical  kiln  conditions  in  drying  2  inch  thick  fir  are  as 
fellows;   The  wood  is  given  a  preliminary  steaming  for  several 
hours,  the  temperature  is  aoout  130  degrees  Fahrenheit,  the  relative 
humidity  of  the  air  is  100  %  and  the  moisture  in  the  7/ood  about 
60  %.   The  object  of  this  preliminary  treatment  is  to  soften  the 
surface  in  case  it  iias  been  casehardened  and  also  to  facilitate  the 
transmission  of  water  from  the  interior  of  the  wood.  The  temperature 
then  fir ops  to  110  a  no  the  relative  humidity  of  the  air  decreases  to 
30  %.   The  temperature  is  then  gradually  increased  and  the  relative 
humidity  of  the  air  decreased.  rue  to  these  changes  the  moisture 
in  the  v;ood  is  decreased  gradually  to  about  30  %  at  the  end  of  the 
first  week.  At  the  end  of  twenty  days,  with  the  temperature 
gradually  increasing  to  150  degrees  Fahrenheit  and  the  relative 
humidity  of  the  air  decreasing  to  20%  the  wood  nas  been  reduced  to 
a  moisture  content  of  10^.  An^  caseharcening  that  has  been  produced 
is  then  removed  by  a  final  steaming  of  a  few  hours  duration,  during 
•which  the  temperature  is  loG  and  the  relative  humidity  of  the  air 
is  100^.   This  treatment  increases  the  moisture  content  of  the  wood 
to  \b%,  v;hich  is  again  reduced  to  10$,  by  a  few  hours  drying  under 
the  conditions  ~ust  preceding  the  final  steaming. 

The  moisture  in  ivood  will  tend  to  come  to  equilibrium  with 
that  of  the  air  in  which  it  is  stored.   Kiln-dry  vrood  (about  Q%_ 
moisture)  will  reabsorb  water  if  stored  under  open-air  sheds  so  that 


Civil  Engr-8.  Assignment  4.  Page   15 

its  moisture  content  will   be  about   15?o-      The  time   required   for   such 
readjustment  depends  upon  the   size   and   shape   of  the  pieces.     Air-dry 
wood   if  stored   in  a  wood -working  shop  will  tend  to  come  to  a  moisture 
content   of  about  6  %.        This  shows  that  wood   is  a  hygroscopic   sub- 
stance.     Since  changes   in  the  moisture  content  produce  changes   in 
the  dimensions   of  cut   lumber   it   is  essential  that  the  moisture  con- 
tent  of  the  rvood  at  the   time    it   is  used   in  cabinet  work  and   other 
exact  construction  be  the   same   as   it  would   be   under  conditions  of 
later  use.      High-grade   furniture    is  varnished   or  given  other   surface 
treatment   on  all  exposed    surfaces   (back  and  underneath)   so  as  to  re- 
duce  the   tendency  of  the  thoroughly-seasoned  wood  to  absorb  water, 
which  would  cause   it  to  swell,   or  to  give   off  moisture  and  produce 
shrinkage.        paraffin  has  been  found  to  be  the  most  effective  sub- 
stance used  to  treat  air-dry  wood   so  as  to  prevent   shrinkage  and 
spelling  when  the  wood   is  subjected  to  atmospheres  of  variable 
humidities. 

The  table  at  the   Dottom  of  page   152   is  not   important. 
Shrinkage  and    its  effects:-       Study  Article   161.      The   removal  of 
free  water  reduces  the  weight   of  wood   but   it  does  not  affect  the   other 
properties.      When  all  the  i'ree  water   is  removed  the   fiber-saturation 
point    is   reached.      Further   decrease    in  water  content  causes  wood   to 
shrink.      3ee  Figure    12   on  page    156.      The   fiber -saturation  point 
usually  ranges   from  25  to  "50%  of  the   dry  weight   of  the  wood.      The 
common  defects  produced  by  improper   seasoning  are  checking,   case- 
hardening,   honeycombing,   and  warping.        Each  of  these   defects   is  ex- 
plained   in  this  article. 


Civil  ringr-8.  Assi^ruient  4.  page  16. 

Amount  of  shrinkage;-   ST-udy  Article  162.  Wood  in  an  air -dry  con- 
dition has  reached  about  one-half  of  its  possible  shrinkage.  Length- 
wise shrinkage  is  negligible  because  the  thickness  of  the  end  walls 
of  the  wood  elements  is  very  small  vhen  compared  to  the  length  of 
these  elements.   Shrinkage  in  a  direction  tangential  to  the  annual 
rings  is  about  twice  as  great  as  in  a  radial  direction.   Consider- 
able force  is  developed  when  confined  wood  s'/ells  due  to  the  ab- 
sorption of  water.  This  is  strikingly  shown  in  an  illustration  in 
Engineering  news,  70,  615,  September  25,  1S13.   Slabs  of  oak  veneer- 
ed with  maple  were  stacked  in  a  basement  to  "within  1  inch  of  the 
lower  side  of  a  12  by  24  inch  reinforced  concrete  beam  which  formed 
part  of  the  first  floor  framing.   The  wood  was  saturated  during  a 
flood  which  caused  it  to  swell.   The  force  developed,  raised  the 
beam  3  inches  at  the  point  of  contact  making  its  replacement  neces- 
sary.  The  shrinKage  from  green  to  over-dry  condition  for  different 
species  of  wood  is  given  in  Table  I,  which  faces  page  196. 
principal  native  woods:-   Study  Articles  167,  168,  173,  174,  185, 
and  189.   They  give  data  on  Western  Yellow  Pine,  Sugar  Pine, 
Douglas  Fir,  Western  Hemlock,  Redwood,  and  Western  Cedar  respectively. 
These  are  the  principal  species  of  wood  grown  on  the  pacific  Coast. 
Article  164  descrioes  Southern  Yellow  pine  which  is  an  important 
species  of  wood;  in  its  properties  and  uses  it  resembles  our 
Douglas  Fir. 

Read  the  other  articles,  not  listed  aoove,  up  to  Article  197. 


Civil  Eugr-8.  Questions  to  Assignment   5.  page    17 

1.  Name  the   principal  woods  grown  in  the  pacific  Cost  forests. 

2.  Distinguish   between  wood ,  timber,   and    lumber. 

\^ 

3.  Sketch  the  cross-section  of  a  tree  and    show  the   bark,   heart- 
wood,   cambium,  pith,    summer  wood,    sapvvood ,   and   spring  wood. 

4.  What  are   the  common  defects   in  structural  timber? 

5.  What   is  the   approximate  weight   of  air-dry  wood?     (Be   sure  to 

give  unit   of  measure) 

6.  What  are  the   reasons  for   seasoning  wood? 

7.  How   is  Tf:ood    seasoned? 

8.  What   is  the   fiber-saturation  point?     What   is   its  significance? 


UNIVERSITY  OF  C.JL, IF OR1-J JA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials   of  Engineering  Construction 
Civil  En^r-a.  Professor  C.   T.    Wiskocil 

Assignment   5= 

DETERIORATION  AMD  PRESERVATION  OF  WOOD 

Reading  Assignment:-  Johnson's  ksterials  of  Construction,  Chapter  V, 
pages  179  to  194  inclusive. 

The  Durability  of  Wood  :-  The  durability  of  wood  depends  upon  the 
conditions  under  which  it  is  used.   The  life  of  Sycamore  lumber, 
when  placed  under  conditions  which  subject  it  to  decay,  is  from  three 
to  five  years.  Weiss,  in  his  book,  Preservation  of  Structural  Timbers, 
gives  an  illustration  of  an  Egyptian  coffin  of  Sycamore  dating  from 
the  XII  dynasty  (2000  -  1788  B.C.;  which  is  still  in  perfect  condi- 
tion. When  wood  is  Kept  dry  its  resistance  to  decay  is  indefinite. 

Black  locust  and  osage  orange  are  probably  the  most  durable 
woods.   Their  life  is  estimated  as  being  over  15  years,  even  under 
adverse  conditions.   They  are  used  principally  for  planing  mill 
products,  vehicle  and  vehicle  parts,  and  ship  and  boat  construction. 
The  life  of  redv/ood  ~nd  cypress  is  from  12  to  15  years  under  similar 
conditions.   These  woods  are  used  principally  for  planing  luill 
products  and  general  cill  work.   The  amount  of  cypress  used  is  about 
si::  times  that  of  redwood.   Redv;ood  is  known  to  have  lasted  for 
much  longer  periods.   Stakes  2  by  3  inches  in  section  driven  by  the 
U.S.  Coast  and  Geodetic  Survey  along  the  California  coast  in  1874 
were  found  in  a  fair  state  of  preservation  in  1921,  47  years  after 
having  been  driven  into  the  ground.   Large  redwood  sills  under  a 


Civil  ^ngr-8.  Assignment  5.  Page  2. 

bridge  pier  near  Eealdsburg,  California,  were  recently  (December 
1921)  found  to  be  in  a  perfect  state  of  preservation,  35  years  after 
being  placed  in  a  position  which  was  aucve  low  water  level. 
Douglas  fir  and  southern  yellow  pine,  the  principal  structural  woods, 
have  an  estimated  life  of  S  to  11  years  when  placed  under  conditions 
subjecting  them  to  decay. 

In  general,  sapwood  is  less  resistant  to  decay  than  heartwood, 
and,  "when  used  without  preservative  treatment  in  situations  favoraole 
to  decay,  sapwocd  is  likely  to  have  much  shorter  life  than  heart-wood. 
But  when  properly  treated  sapwood  and  heartwood  are  practically 
equal  in  resistance  to  decay. 

Some  woods  are  more  duraole  than  others.  The  reason  for  this 
difference  is  not  Known.  Density  does  not  seer,  to  oe  a  criterion 
of  durability.   Durability,  however,  can  be  judged  by  the  presence 
of  sapwood,  the  moisture  content,  the  presence  of  sap  stain, 
structural  defects,  and  the  amount  of  resin,   pronounced  variations 
in  color,  especially  when  wood  is  spotted  or  streaked,  indicate  in- 
cipient decay.  Resin  keeps  out  moisture  and  air  and  thus  acts  as 
•^^ 

a  preservative.  Fence  posts  having  a  high  pitch  content  last  longer 
than  those  having  less  pitch.   Such  defects  as  checks.. and  knot 
holes  offer  places  for  the  lodgement  of  the  spores  of  fungi  and  form 
starting  places  for  decay. 

The  color  of  cypress  was  thought  to  be  a  criterion  of  its 
resistance  to  decay.  But  investigations  by  the  U.S.  Forest  products 
Laboratory  have  proved  that  the  color  of  the  wood  makes  little 


Civil  Engr-8.  Assignment  6.  Page  3. 

difference.   If  durability  is  desired  it  is  important  to  select 
heartwood  of  cypress  regardless  of  its  color. 

The  moisture  content  of  wood  to  be  used  in  building  construc- 
tion, particularly  in  poorly  ventilated  places,  is  of  importance 
because  poor  ventilation  is  favorable  to  the  attack  of  the  so-called 
"dry  rot".   (See  discussion  on  page  181).   Mill  construction  with 
poorly  seasoned  wood  has  been  known  to  have  become  infected  within 
a  year  or  two  after  completion,  whereas  well  -seasoned  wood  has  re- 
sisted decay  under  similar  conditions  for  more  than  ten  years.  The 
term  "dry  rot"  is  frequently  applied  to  any  decay  in  comparatively 
dry  wood.  Dry  rot,  however,  is  the  result  of  the  attack  of  the 
house  fungus,  merulius  lachryraans,  which  is  frequently  found  growing 
in  dry  wood  without  any  apparent  supply  of  moisture.  The  U.S. 
Forest  Products  Laboratory  has  proved  that  this  fungus  will  not 
grow  in  thoroughly  dry  wood  out  it  will  germinate  in  moist  wood  and 
make  its  way  for  long  distances  into  dry  wood,  drawing  the  necessary 
water  from  the  moist  wood  through  a  system  of  minute  porous  strands. 
Wood  in  the  advanced  stage  of  dry  tot  is  shrunken,  yellow  to  brown 
in  color,  and  so  brittle  that  it  can  easily  be  crushed  into  powder. 
The  dry  rot  fungus  is  active  throughout  this  country  attacking  coni- 
ferous woods  more  commonly  than  the  dicotyledons. 

The  following  are  the  principal  causes  for  the  rapid  deteriora- 
tion of  wood  in  buildings: 

1.  The  use  of  green  lumoer. 

2.  Allowing  lumber  to  get  wet  during  construction. 

3.  Allowing  lumber  to  absorb  moisture  after  the 
building  is  completed,  because  of  leaks  or  lack.. 
of  ventilation. 

4.  The  use  of  lumber  containing  too  much  sapwood. 


Civil  Engr-3.  Assignment  5.  page  4. 

The  avoidance  of  these  conditions  ^ill,  as  a  rule,  prevent  decay. 

In  certain  cases,  however,  decay  can  only  be  prevented  by  preservative 
treatment. 

The  chief  causes  for  deterioration  are  decay,  marine  borers, 
insects,  mechanical  abrasion,  and  fire.   Birds  and  alxali  soils  cause 
deterioration  but  it  is  estimated  that  decay  is  the  most  important. 
C opposition  of  Wood:-  Read  Article  202.   In  the  previous  assign- 
ment the  composition  of  wood  was  given  as  lignocellulose ,  which  is 
a  starch-like  substance,  permeated  by  lignin,  resin,  coloring- 
matter,  water,  and  a  small  proportion  of  inorganic  matter. 
Causes  of  Decay :-  Study  Article  203.   The  attack  of  bacteria  and 
fungi  cause  the  decay  of  wood.   Only  a  small  percentage  of  these 
parasites,  v/hich  are  low  forms  of  plant  life,  have  the  ability  to 
decay  wood.  Most  wood-rotting  fungi  thrive  at  temperatures  around 
80  degrees  Fahrenheit;  small  rises  aoove  this  optimum  temperature 
are  often  fatal.   It  is  good  practice  to  heat  newly  completed  wood 
buildings  i:i  order  to  kill  surface  growths  of  fungi,  practically 
all  fungi  survive  the  coldest  winters.   Spores  of  fungi  are  known 
to  have  remained  alive  for  8  years  when  in  a  dry  condition. 
Insects:-   Study  Article  204.   Insects  damage  wood  in  any  form  by 
cutting  out  ourrows  or  galleries.   Borers  like  termites  and  powder- 
post  borers,  enter  the  stick  of  v:ood  through  a  small  hole  and  then 
excavate  winding  burrovs,  whose  extent  cannot  be  estimated  by  sur- 
fact  indications.   White  ants  or  termites,  black  ants,  carpenter 
bees,  and  powder-post  borers  are  the  principal  wood  boring  insects. 
It  has  been  reported  (1922)  that  in  some  localities  near  Los  Angeles, 
California,  as  many  as  50$  of  the  cedar  poles  set  by  the  Southern 


Civil  fcngr-8.  Assignment  5.  Page  5. 

California  Edison  Company  prior  to  1910  have  been  attacked  by 
termites.   The  infected  area  extends  from  San  Diego  to  Santa  Barbara 
and  east  to  Red  land d.   The  insects  enter  the  poles  at  the  ground 
line  and  frequently  attack  the  pins  on  the  cross-arms  without  coming 
to  the  surface  of  the  pole.   Creosote  oil  has  been  found  to  be  an 
effective  preservative. 

Marine  Borers  :-   Study  Article  205.   Destruction  by  marine  borers 
during  IS 19  and  1920  in  San  Francisco  Bay  and  the  adjoining  San 
Pablo  Bay  and  Suisun  Bay  has  been  estimated  by  a  committee  of  the 
American  Wood  Preservers1  Association  who  reported  in  "San  Francisco 
B^y  Marine  piling  Survey",  to  be  in  excesc  of  15  million  dollars. 
There  are  three  species  of  moliuscan  borers:  Teredo  navalis, 
Teredo  diegensis,   .  .  .  ,  • and  Xylotraya  setacea,  besides 

tliree  species  of  crustacean  oorers:  Linmoria,  Sphaeroma  and  Chelura, 
active  in  this  region,  tohere  the  attacK  of  these  oorers  is  severe, 
untreated  piles  are  destroyed  in  6  to  8  months.   In  otner  places 
they  may  last  2  to  4  years.   Properly  creosoted  piles  of  Douglas  Fir 
have  a  life  of  aoout  25  years-  Destruction  of  creosoted  piles 
has  been  the  result  of  untreated  -wood  being  exposed  to  attacK  by 

damage  to  the  surface  in  handling  or  placing  the  piles.   Various 

not 

kinds  of  protection  to  -wood  piles  have/ been  very  effective.   Pre- 
servative treatment  with  creosote  has  been  most  satisfactory.   The 
attacks  of  marine  oorers  is  not  new.   They  were  known  to  the  ancient 
Romans.   The  following  note  was  taken  from  Voyages  and  Travels, 
Vol.  II,  C.R-  Beazley,  in  regard  to  the  ships  sent  out  to  discover 


Civil  tngr-8.  Assignment  5.  Page  6. 

the  Northwest  Passage  during  the  reign  of  Henry  VI: 

"They  cover  a  piece  of  the  keels  of  the  shippe  with  their 
sheets  of  leade,  for  they  had  heard  that  in  certaine 
partes  of  the  ocean  a  kindo  of  wormes  is  bredde ,  which 
many  times  pearceth  and  eateth  through  the  strongest  oake 
that  is." 

Other  Deteriorating  Influences;-   Read  Article  206.  Mechanical 
abrasion  and  fire  are  important  destroyers  of  wood,  whereas  alkali 
soils,  and  birds  are  only  minor  causes  of  deterioration. 
The  Need  of  Preservation \-   Read  Article  207.   The  idea  of  wood 
preservation  is  not  new.   Pliny  writes  thrt  in  his  time,  wood  was 
protected  from  attacks  by  worms  by  treating  it  with  garlic  boiled  in 
vinegar.   The  early  Greeks  and  Romans  used  the  oils  from  Cedars 
and  Junipers  for  their  antiseptic  value.   These  oils  were  rubbed 
over  the  surface  of  the  wood  to  f  be, preserved.   The  Britons  made 
various  attempts  to  protect  their  wooden  warships  from  decay.  Wood 
preservation  is  now  practiced  all  over  the  world.   The  necessity  of 
preservation  is  given  in  the  text  (Article  2o7j.   There  are  two 
methods  of  protecting  wood  from  destruction  by  living  organisms. 
The  first  is  to  control  the  conditions  necessary  for  life  and  thus 
inhibit  their  growth.   This  means  the  control  of  the  temperature  and 
the  moisture  content,  which  is  not  practical  in  the  commercial  use 
of  wood.   The  second  method  is  to  inject  a  material  which  will  kill 
or  poison  the  organisms  themselves  or  the  enzymes  through  which 
they  accomplish  their  destruction.   This  latter  method  is  now  the 


Civil  Engr-8.  Assignment  5.  Page  7. 

standard  practice. 

The  Relation  of  Structure  to  the  Penetration  of  Preservatives :- 
Study  Article  208.  This  article  shows  the  effect  of  the  various 
structures  upon  the  diffusion  of  preservatives  and  indicates  why  all 
woods  cannot  be  given  the  same  treatment  if  uniform  results  are  to 
be  expected.  Douglas  Fir,  as  noted,  cannot  be  easily  impregnated. 
It  is  now  being  mechanically  perforated  so  that  a  uniform,  pre- 
determined, penetration  of  preservative  can  be  secured. 
The  Treatment  of  Timber  before  Preservation:-   Study  Article  209. 
Wood  is  thoroughly  seasoned  before  being  given  preservative  treat- 
ment. The  preliminary  treatment  is  described  in  this  article. 
Superficial  Treatments:-   Read  Articles  210  to  213  inclusive. 
Superficial  processes 'simply  give  the  wood  a  thin  surface  coating  of 
preservative.   Timber  so  treated  is  apt  to  have  the  protecting  coat- 
ing broken  either  by  abrasion  or  checking  which  exposes  untreated 
wood  and  subjects  the  entire  piece  to  decay. 

Superficial  processes  are  inexpensive  and  are  used  only  when 
small  quantities  of  wood  are  treated.  Dipping  is  more  effective 
than  brush  treatment.  Recent  tests  by  the  U.S.  Forest  Products 
Laboratory  have  proved  that  charred  posts  were  less  durable  than 
untreated  ones.   The  charred  surface  is  usually  not  a  solid  cover- 
ing.  It  is  checked  through  in  many  places.   If  seasoned  posts  are 
charred  the  charring  does  not  reach  to  the  oottom  of  the  season 
checks  which  are  always  present.   If  green  posts  are  charred  season 
checks  open  up  through  the  charred  exterior.   In  either  case  the 


Civil  Engr-8.  Assignment   5.  Page  8. 

* 
uncharred   interior   is  exposed  to  infection  and  will  decay  as  rapidly 

as  untreated  wood.      Charring  deep  enough  to  resist  decay  would  un- 
doubtedly weaken  a  post   of  ordinary   size. 

Non-pressure  Processes  of  Impregnation;-       Study  Articles  214  to  216 
inclusive.      Non-pressure  methods  are  carried   on  in  open  tanks.     They 
insure  a  better  penetration  than  is   ootained  by  the   superficial 
processes.     Open-tank  and  Kyanizing  are  the  tv;o  non-pressure   im- 
pregnation processes  now   in  use.      They  differ   from  pressure  processes 
in  that  the    latter  use  pressures  aoove  atmospheric  to  force  the  pre- 
servative  into  the  wood.      Farmers  and  mine  and  telephone  companies 
are  the  principal  users   of  open-tadk  methods   of  preserving  wood. 
Mercuric   chloride  was   first  used  as  a  wood   preservative   in  1705.      The 
process  of  preservation  in  which  this   salt   is  used  was  patented   in 
England   by   John  H.   Kyan  in  1832.      It  was   introduced    into  the  United 
States  about   1840  and   is  said  to  be  the   oldest  method   of  treating 
wood  now  practiced   in  this  country.      The  details   of  the  process  are 
given  in  Article   216. 

Pressura  Processes   of  Impregnation:-     Study  Articles  217  to  223   in- 
clusive.     Pressure  processes  use  pressures  aoove   atmospheric  to  force 
preservative    into  the  wood.      The  fie the  11  process   (Article   219)    is 
named  after   John  fietheli  who  took  out  patents   in  England   in  1838. 
It   is  commonly  called  the   full-cell  process.      Green  or   seasoned 
wood   can  be   treated   by  this  method.      It    is  considered  the    standard 
process  of  treating  wood  with  creosote.      The  process  has  been  modi- 
fied  because   of  its  excessive  use  in~  preservation. 


Civil  Engr-8.  Assignment  5.  Page  9. 

The  boiling  process  (Article  220)  was  patented  in  the  United 

States  by  W.G.  Curtis  and  J.D.  Isaacs  in  1895.  With  the  exception 

m 
of  the  preliminary  treatment  which  the  wood  is  given,  it  resembles 

the  Bethell  process. 

The  Lowry  process  (Article  222)  is  sometimes  called  the  empty- 
cell  process.   It  was  patented  in  the  United  States  by  C.B-  Lowry 
in  1906. 

The  Rueping  process  (Article  220)  is  also  called  an  empty- 
cell  process.   It  was  patented  in  1902. 

The  Card  process  (Article  223)  was  patented  in  1906  by  J.B. 
Card. 

The  Burnett  process  (article  219)  was  patented  in  England 
in  1838  by  William  Burnett.   It  is  the  standard  zinc  chloride 
process. 

Study  these  pressure  methods  and  be  able  to  outline  the 
process  and  give  the  kind  of  preservative  used  in  each. 
Preservatives  :-   Study  Article  224,  which  describes  the  preservatives 
commonly  used  for  treating  wood.   The  principal  requirement  for  a 
good  preservative  is  that  it  be  able  to  kill  the  organisms  which 
attack  wood  or  destroy  the  agents  (enzymes)  through  which  these 
organisms  work.   In  addition  the  preservative  must  be  soluble  in  the 
body  fluids  of  the  organisms.   Since  organisms  which  attack  wood 
have  water  as  their  chief  body  fluid,  it  is  necessary  that  a  material 
to  be  toxic  must  be  soluble  in  water  to  a  certain  extent.   In  this 
respect  oil  solutions  and  inorganic  salts  must  De  similar.   Wood  im- 
pregnated with  zinc  chloride  has  all  the  toxic  zinc  in  solution 


Civil  Engr-8.  Assignment   5.  page   10. 

and  the   concentration  of  this   zinc   becomes  weaker  and  weaker  by 
any  leach;.ng  to  which  the  wood  may  be   subjected.      Creosote   oil,  which 
may   include  hydrocarbons   (such  as  benzene,   toluene  and  naphthalene) 
or  tar  acids   (such  as  the  cresols  and  naphthols)   or  tar   bases   (such 
as  quinoline  and   isoquinoline)    or  a  comoination  of  all  three,    is 
(according  to  Baternan)   divided   into  two  groups.     The  first  one  con- 
tains those   oils  that  are   sufficiently  soluble   in  water  to  render 
their  water   solutions  capable   of  -killing  the  wood -destroy ing 
organisms  and   are  celled  toxic   oils.      'Ihe    second   group,  which  are 
called  non-toxic   oils,   are   not  sufficiently   soluble  to  produce  a  toxic 
water   solution.      Toxic   oils  are  completely   soluble   in  non-toxic   oils 
and   are   partially   soluble   in  water.    Ihe   toxic   oils,   therefore,   di- 
vide themselves  between  the  water   and  the  non-toxic   oils   in  such  a 
manner  that  their   concentration  in  water  and  the  non-toxic   oils   is 
in  proportion  to  their   solubility   in  the   respective  media.      The  non- 
toxic   oils  act  as  a  reservoir  for  the  toxic   oils.     Assume  a  toxic 
oil  as  being  50  times  as  soluole   in  a  non-toxic   oil  as   it   is   in 
water.     Take  a   10$  solution  of  the  toxic   oil   in  the  non-toxic   oil. 
When  such  a  solution  comes  in  contact  with  an  equal  volume   of  water 
the   concentration  of  the  water  will  be  0.2$»      If  the  toxic    limit   of 
the  water   solution  is  0.05$.  then  the  water   solution   is  four  times 
as  toxic  as   is  necessary  to  kill.      Suppose  that  this  water   is  with- 
drawn and  an  equal  amount   added,  which   in  turn  takes  up   its  propor- 
tion of  toxic    oil.     This  change   of  water  could  take   place   seventy 
times  before  the  toxicity  of  the  water  would   be   below         Killing 
point.     This   is  Bateman's  theory. 


Civil  Engr-8.  Assignment  5.  Page  11. 

In  actual  practice  the  rapidity  of  this  change  depends  upon 
the  conditions  under  which  the  wood  is  used.   If  alternately  wet  and 
dry,  such  as  piling  between  high  and  low  tides,  a  high  rate  of  deple- 
tion of  preservative  could  be  expected.  A  much  slower  rate  of  solu- 
tion would  take  place  in  dry  places,  such  as  those  of  telephone 
poles. 

The  difference  between  oil  and  inorganic  salt  preservatives 
according  to  this  theory  is  in  the  method  of  retaining  the  reserve 
supply  of  toxic  materials.   Zinc  chloride  has  no  reserve  supply, 
all  of  the  material  is  soluble  in  the  usual  amount  of  moisture 
present  in  air-dry  wood. 

Bateman  has  proved  his  theory  by  experiments  with  tar  acids. 

Study  this  theory  carefully  and  compare  it  "with  statements 
in  Article  224  in  the  text. 

Article  225  is  relatively  unimportant  -  omit  it. 


Civil  Engr-8.  Questions  to  Assignment  5.  Page   12. 

1.  What  are   the  principal  causes  for  the  deterioration  of  woods? 

2.  What  causes  wood   to  decay? 

3.  What   is  dry-rot?     How  can  it  be  prevented? 

4.  Differentiate  between  the  attach  on  wood  piles   of  the   limnoria 

and  the" teredo. 

5.  What  methods  are  used  to  preserve  wood? 

6.  Outline  the  full-cell  process.  What  are  its  disadvantages? 

7.  Name  the  preservatives  commonly  used  for  impregnating  wood  as 

protection  against  attack  of  living,  organisms. 

8.  Explain  why  creosote  is  more  effective  than  zinc  chloride  in 

preserving  wocd  ?;hen  it  is  subjected  to  alternate  wetting 
and  drying. 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 
Civil  Engr-8.  Professor  C-T-  Wiskocil 

Assignment  6. 
The  Mechanical  Properties  of  Vfood 

Introduction:-  Read  Article  226.  The  effective  use  of  wood  requires 
a  thorough  knowledge  of  the  factors  which  affect  its  mechanical 
properties.  Some  of  these  factors  have  already  been  studied  but  in 
•this  assignment  their  relative  importance  will  oe  emphasized. 

When  comparing  the  general  quality  and  the  strength  of  "wood, 
the  term  "strength"  must  be  carefully  defined.   In  the  strict  sense, 
strength  means  the  ability  to  resist  a  definite  stress  or  load,  as 
compressive  strength*  Generally  the  term  strength  may  have  a  number 
of  meanings,  depending,  upon  how  the  wood  is  used.   In  the  case  of 
beams,  transverse  or  bending  strength  is  implied,  in  columns  com- 
pressive strength  is  meant,  whereas  for  implement  handles  both 
hardness  and  toughness  are  included  in  the  term  strength* 

Table  I,  in  the  text,  gives  comparative  values  of  the  mechani- 
cal properties  of  woods.  A  more  comprehensive  compilation  of  test 
results  is  given  in  "MECHANICAL  PROPERTIES  OF  WOODS  GROVnN  IN  THE 
UNITED  STATES"  by  Newlin  and  Wilson,  Forest  Service  Bulletin  556, 
United  States  Department  of  /Agriculture,  from  which  the  following 
table  is  abstracted : 


11  Ln-,r-8. 


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Civil  Engr-S.  Assignment  6.  page  5. 

Table  I  is  an  excellent  reference.   If  recent  data  are  need- 
ed Forest  Service  Bulletin  556  will  be  found  to  be  more  complete. 
It  is  a  good  idea  to  take  some  common  species  of  wood  such  as 
Douglas  Fir  and  remember  the  data,  given  in  the  abstracted  table  in 
these  notes,  for  the  wood  in  the  green  condition.   Most  of  the  tests 
from  which  such  values  are  obtained  were  made  at  the  Forest  products 
Laboratory  at  Madison,  Wisconsin  (see  page  195  in  text). 

The  test  pieces  v;ere  all  straight -grained  and  free  from  de- 
fects, such  as  knots,  shakes  and  checks,  and  in  the  same  condition 
of  seasoning.   The  values  given  were  based  on  about  130,000  tests 
on  126  species  of  wood.  Data  are  given  for  green  and  air  dry  con- 
ditions because  the  properties  of  all  species  are  not  changed  in 
the  same  proportion  bj.  drying  and  all  the  properties  are  not  equally 
affected,  .air-dry  woods  should  have  the  same  moisture  content  in 
order  to  be  strictly  comparaole,  but  in  the  case  of  wood  in  the 
green  condition,  even  though  quite  different  for  the  different 
species,  the  moisture  content  is  adov.a.  the  fiber  saturation  point 
and  above  this  point  changes  in  moisture  do  not  affect  the  strength. 
Tests  on  individual  pieces  may  be  expected  to  vary  from  "t  j  to 
"i  14^  from  the  values  given  in  these  tables. 

Compressive  Strength:-   btudy  Article  227.   The  compressive  strength 
parallel  to  the  grain  is  important  in  estimating  the  strength  of 
columns  and  struts.   It  is  determined  by  tests  on  2  by  2  by  8  inch 
specimens.  A  compressometer  with  a  6  inch  gage  length  is  used  so 
that  the  elastic  limit  and  the  modulus  of  elasticity  can  be  determin- 
ed. A  typical  curve  is  shovjn  in  Figure  6  on  page  210.   The  maximum 


Civil  Engr-8.  Assignment  6.  Page  4. 

strength  is  more  easily  determined  than  elastic  limit  strength  and 
is  also  less  variable.  Working  stresses  must  be  well  below  the 
elastic  limit.  For  columns  in  dry  interior  construction  having  a 
length  less  than  10  times  the  least  dimension,  a  working  stress  of 
about  1/3  of  the  c empress ive  strength  of  green  wood  is  used. 

Wood  is  also  tested  in  compression  perpendicular  to  the 
grain.  The  specimen  is  2  by  2  by  6  inches  with  the  load  applied 
through  a  steel  plate  2  inches  wide.  The  area  under  load  is,  there- 
fore, 4  sq  inches.  A  def lectometer  of  the  type  shown  in  Figure  48 
on  page  89  is  used  to  get  a  stress-deformation  curve  similar  to  the 
one  shown  in  Figure  6  on  page  210.   Only  the  stress  at  the  elastic 
limit  is  determined  because  this  is  the  maximum  stress  that  can  be 
applied  without  injury.   Greater  loads  crush  the  specimen  without  a 
definite  point  of  failure.   Furthermore,  the  deformation  measure- 
ments are  easily  obtained  so  that  the  elastic-limit  determination  is 
a  simple  one.   Strength  perpendicular  to  the  grain  is  developed  in 
bearing  areas  of  beams,  railroad  ties,  and  in  any  construction  where 
the  load  is  similarly  applied.   A  working  stress  of  approximately 
2/3  the  elastic  limit  of  green  wood  may  be  safely  used  in  dry  in- 
terior construction.   Omit  Tables  2  and  3;  They  are  useful  only 
when  specific  information  is  needed. 

Tensile  strength  of  wood:-  Read  Article  228.   The  tensile  strength 
of  wood  parallel  to  the  grain  is  rarely  determined.  The  Forest 
Service  tests  the  tensile  strength  perpendicular  to  the  grain.   The 
form  of  specimen  and  the  manner  of  loading  are  shown  in  Figure  1 
on  page  201.   The  data  from  this  test  are  of  value  in  establishing 


Civil  Engr-8-  Assignment  6.  Page  5. 

the  resistance  of  wood  to  the  splitting  action  of  bolts  and  other 
fastenings. 

The  shearing  strength  of  wood:-   Read  Article  220.   Shearing  stress 
parallel  to  the  grain  is  developed  in  most  structural  uses  of  wood. 
It  is  of  importance  in  beams  (see  Figure  2  on  page  202),  where  it 
is  called  horizontal  or  longitudinal  shear.   It  is  also  of  importance 
in  the  design  of  wooden  joints  (see  Figure  3  on  page  203).  Shearing 
stress  across  the  grain  is  rarely  listed.  The  specimen  and  the 
method  of  making  the  shearing  test  parallel  to  the  grain  are  shown  in 
Figure  14  on  page  63.   Longitudinal  shear  is  greatest  at  the  neutral 
surface  of  the  beam  and  is  affected  by  checks  and  shakes  which  re- 
duce the  effective  area  resisting  shearing  stresses.   These  defec^s 
must  be  expected  in  structural  timber;  therefore  safe  working 
stresses  for  longitudinal  shear  in  beams  are  about  1/8  of  the  values 
obtained  from  tests  on  clear,  straight  grained  pieces.  For  joints 
and  small  details  where  checks  and  shakes  can  be  avoided  the  work- 
ing stress  may  be  increased  to  1/4  the  strength  of  green  wood.   Omit 
Tables  4  and  5. 

Transverse  strength  of  wood  .--   Study  Article  230.  This  property 
of  wood  is  determined  by  the  static  bending  test.   The  specimen  is 
2  by  2  by  30  inches,  tested  on  a  23-inch  span.   The  load  is  applied 
at  the  center.  A  def lectometer  is  used  so  that  a  load-deflection 
curve  similar  to  that  in  Figure  6  on  page  210  can  be  drawn.  Large 
timbers  are  loaded  at  the  third-points  as  shown  in  Figure  2  on  page 
202.   The  static  bending  test  is  easily  made  and  yields  important 
data.  Working  stresses  in  bending  must  be  below  the  elastic  limit 


Civil  Engr-8.  -  ssignment  5. 

for  if  wood  is  stressed  to  its  elastic  limit  in  static  bending  it 
will  ultimately  fail.  Determinations  of  elastic  limit  are  not  so 
reliable  as  those  of  the  maximum  fiber  stress,  ^'hich  is  known  as 
the  modulus  of  rupture.  Working,  stresses  should,  therefore,  be  based 
on  the  latter.  Remember  that  the  modulus  of  rupture  is  not  the 
actual  fiber  stress,  because  it  is  based  upon  a  theory  which  is 
valid  only  when  the  elastic  limit  is  not  exceeded. 

A  green  timber  relatively  free  from  defects  will  have  a  modu- 
lus of  rupture  of  about  3/4  as  large  as  small  deter  pieces  cut  from 
it. 

Safe  working  stresses  for  structural  timber  in  interior  con- 
struction should  be  about  1/5  the  modulus  of  rupture  for  green  wood. 
For  exposed  construction  the  working  stresses  should  be  lower. 
Strength  in  longitudinal  shear  must  also  be  considered  when  design- 
ing wooden  beams.    Omit  Taole  6. 

The  time  element  in  loading  wood:-   Read  Article  231.   The  strength 
of  wood  is  affected  by  the  rate  at  which  the  test  load  is  applied. 
The  speed  of  testing  should,  therefore,  be  considered  (See  the 
Forest  Service  program  as  given  in  this  article).   The  most  import- 
ant fact  in  this  article  is  that  the  resistance  of  wood  under  per- 
manent loads  is  less  than  7; hen  it  is  under  temporary  loads.   It 
takes  about  50^  of  the  ultimate  load  as  applied  in  a  testing  machine 
to  cause  failure  if  permanently  applied.   This  is  another  reason 
why  working  stresses  are  so  low  when  compared  with  ultimate  strength 
as  determined  by  tests  made  in  a  testing  machine. 


Civil  Engr-8.  Assignment  6.  Page  7. 

Stiffness  and  other  mechanical  properties:-   Study  Articles  232,  253, 

234  and  235.   Stiffness,  which  is  measured  Dy  the  modulus  of  elas- 

£ 

ticity,  has  an  average  value  of  aoout  1,200,000  Ib.  per  sq.  in.   In 
the  case  of  a  beam  the  modulus  of  elasticity  is  a  measure  of  its 
resistance  to  deflection.  The  importance  of  this  property  is  in- 
dicated in  Article  232.   Green  wood  is  not  so  stiff  as  air  seasoned 
wood.   Stiffness  is  usually  determined  in  the  static  bending  test. 

Toughness  is  sometimes  defined  as  the  ability  of  wood  to 
withstand  impact  loads.   Impact  loads  are  sustained  by  spokes  of 
an  automobile  wheel,  ax  or  implement  handles  and  athletic  goods 
such  as  baseball  bats.  A  measure  of  toughness  is  ootained  by  the 
impact  bending  test  and  the  energy  of  rupture  in  the  static  bending 
test.   Impact  bending  is  made  on  a  2  by  2  by  30  inch  specimen 
tested  on  a  28  inch  span.   The  machine  used  is  shown  in  Figure  19 
on  page  66.  A  50  Ib.  hammer  is  usually  used.  The  height  of  drop 
to  produce  failure  indicates  the  toughness  of  the  wood  as  stated 
in  Article  233.   Wood  in  the  green  condition  is  tougher  than  after 
it  is  seasoned.  A  suddenly  applied  load  has  tvrice  the  effective 
force  as  -when  gradually  applied.   The  fiber  stress  at  the  elastic 
limit  in  impact  is  approximately  douole  the  fiber  stress  at  the 
elastic  limit  in  static  bending.   Stated  in  another  way:  a  small 
beam,  if  the  load  is  suddenly  applied,  will  deflect  twice  as  much 
as  under  the  same  load  gradually  applied  -  provided  the  loads  are 
under  the  elastic  limit. 

The  height  of  drop  is  an  aroitrary  value  but  it  gives  an 
excellent  comparison  of  the  toughness  of  the  different  woods  tested. 


Civil  Engr-8.  Assignment  6.  page  8. 

While  cleavability  is  an  important  property  in  some  uses  of 
wood,  it  is  not  usually  tested.  A  special  test  for  it  is  described 
in  Article  234. 

The  hardness  of  wood  is  frequently  determined.  The  method  is 
to  measure  the  load  required  to  embed  a  0.444  inch  ball  to  1/2  its 
diameter  in  the  wood.   The  test  is  applied  to  end,  tangential,  and 
radial  surfaces.  Radial  and  tangential  hardness  are  quite  similar 
and  are  called  sice  hardness  as  distinguished  from  end  hardness, 
•which  is  usually  much  greater.   Hardness  is  an  important  quality  in 
wood  used  for  paving  blocks,  floors,  railroad  ties,  and  furniture. 
Read  Article  235  in  the  text. 

• 

Conditions  affecting  Lechanical  Properties  of  timber:-   Read  care- 
fully Articles  236  to  245  inclusive.  Differences  in  the  strength 
of  wood  are  usually  due  to  differences  in  defects,  moisture  content, 
or  density.   Defects,  while  discussed  at  this  time,  would  be  more 
properly  taken  up  under  the  subject  of  grading.   The  most  important 
conditions, then,  which  affect  the  mechanical  properties  of  wood  are 
moisture  and  density. 

Density  or  specific  gravity  was  defined  under  the  subject  of 
physical  properties  of  wood.   Apparent  specific  gravity  (the  ratio 
of  the  weight  of  a  given  volume  of  wood  to  the  weight  of  an  equal 
volume  of  water)  is  an  indefinite  quantity  unless  the  circumstances 
under  which  it  is  determined  are  specif ied, because  the  weight  in  a 
given  volume  changes  with  the  shrinkage  and  swelling  caused  by 
changes  in  the  moisture  content.   Specific  gravity  is  based  on  the 


Civil  Bngr-8.  .assignment  6.  page  fc, 

volume   of  wood  when  green,   and  when  air-dry   or   ov'eft-dry.      Specific 

gravity  based   on  green  volume   is  not  affected  by  the   shrinkage   of 

wood  and   is  therefore  more  reliable  than  air   or   oven  dry   specific 

gravity. 

Note:  Correction  is  made  for  the  amount  of  moisture  in  the  wood. 

Specific  gravity,  aside  from  actual  strength  test  data,  is 
the  most  reliable  criterion  on  the  strength  of  clear  wood.  The 
Forest  Products  Laboratory  examined  seven  species  of  woods,  both 
conifers  and  dicotyledons  and  found  only  a  4  1/2  %  variation  in  the 
specific  gravity  of  the  wood  substance.   The  specific  gravity  of  a 
piece  of  wood  is,  therefore,  a  measure  of  the  amount  of  wood  sub- 
stance it  contains.  The  greater  the  density  the  more  wood  it  con- 
tains and  therefore  the  greater  its  strength.  This  relation  is 
shown  in  Figure  3  on  page  213. 

Since  the  weight  per  cubic  foot  depends  upon  the  moisture  in 
a  green  wood,  it  is  quite  variable.   The  conditions  under  which  it 
is  obtained  should,  therefore,  be  specified. 

The  effect  of  rate  of  growth,  measured  by  the  number  of  rings 
per  in^jis  shown  in  figure  10  on  page  215.   Rate  of  growth  is  ex- 
tremely variable.   The  curves  show  no  definite  relation  between  rate 
of  growth  and  strength.  Wood  which  has  tfrown  slowly  is  usually 
below  average  strength.   In  coniferous  wood  of  very  rapid  growth  the 
strength  is  also  likely  to  be  below  average.   In  the  dicotyledons, 
however,  the  wood  of  rapid  growth  is  usually  above  average  strength. 

The  amount  of  summerwood  in  any  species  is  indicative  of 


Civil  Engr-8.  Assignment  6.  Page  10. 

the  density.  The  amount  of  summerwood  is  measured  along  a  repre- 
sentative radial  line  and  expressed  in  percentage  of  the  entire 
area.  When  the  difference  in  color  between  spring  and  summer 
(early  and  late)  wood  is  not  clear  and  distinct,  accurate  measure- 
ments cannot  be  made  and  the  results  are  of  no  practical  value. 

of 
The  relation  of  the  percentage/ summerwood  to  certain  mechanical 

properties  are  given  in  Figure  12  on  page  216. 

Differences  in  strength  of  wood  as  caused  by  differences  in 
location,  of  growth,  and  of  differences  in  position  in  the  tree 
have  usually  been  overestimated. 

The  influence  of  defects  such  as  knots,  checks,  and  shakes 
is  described  in  Article  240.   Stucly  this  article  carefully. 
Heartwood  and  Sapwood:-   The  difference  between  the  strength  of 

heartwood  and  sapwood  is  not  discussed  in  the  text.   The  following 

recent 
statement  is  taken  from  a/ report  by  the  Forest  Products  Laboratory: 

"in  over  300,000  tests  which  have  been  made  at  the  Forest  products 
Laboratory,  Madison,  Wisconsin,  on  the  various  species  of  wood 
grown  in  the  United  States,  no  effect  upon  the  mechanical  properties 
of  wood  due  to  its  change  from  sapwood  into  heartv:ood  has  ever  oeen 
noticed.   Any  difference  in  the  strength  of  heartwood  and  sapwood 
can  usually  be  explained  by  the  growth  and  density  of  the  wood". 
Comparative  value  of  wood  cut  from  live  and  dead  trees:-   This  sub- 
ject is  not  discussed  in  the  text  but  some  specifications  preclude 
the  use  of  lumber  cut  from  dead  trees.   This  subject  has  been 
studied  at  the  Forest  Products  Laboratory  and  they  report  that  there 


Civil  Engr-6.  assignment  5-  page  11. 

is  no  known  method  by  which  lumber  cut  from  dead' trees  can  "be 
distinguished  from  that  cut  from  live  trees-  Furthermore  all  avail- 
air  13  information  indicates  that  wood  cut  from  insect  or  fire  killed 
trees  is  just  as  good  for  any  structural  purpose  as  that  cut  from 
live  trees  of  similar  quality,  providing  the  wood  has  not  been  sub- 
sequently injured  by  decay  or  further  insect  attack.  Heartwood  in 
a  living  tree  is  entirely  dead  and  in  the  sapwood  only  a  few  cells 
are  alive.  Most  of  the  wood  cut  from  trees  is.  dead,  regardless  of 
whether  the  tree  itself  is  lining  or  not.   Specifications,  instead 
of  providing  that  wood  must  we  cut  from  live  trees,  should  state 
that  mate-rial  showing  evidence  of  decay  or  insect  attack  exceeding 
a  definite  limit  will  not  be  accepted. 

Articles  £42  to  245  are  relatively  unimportant  -  just  read 
them  over-   In  the  case  of  preservatives,  Article  243,  it  would  be 
more  exact  to  say  that  the  effect  of  preservative  treatment  on  the 
strength  of  wood  is  independant  of  the  type  of  preservative  because 
it  is  the  method  or  process  and  not  the  kind  of  preservative  used 
that  affects  the  strength  of  wood.   Creosote,  which  is  the  most 
common  preservative,  does  not  appear  to  effect  the  strength  of  wood, 
A  preservative  process  that  weakens  one  species  of  wood  may  -not 
affect  the  strength  of  another  species.  The  results  are  also 
affected  by  the  form  and  size  of  timber  treated  as  well  as  its  con- 
dition. 

Article  241  -  The  Effect  of  Moisture  on  the  Mechanical 
Properties.  The  relation  between  moisture  content  and  strength  is 


Civil  Engr-8.  Assignment   6.  Page    12. 

clearly  shown   in  Figure   15   on  page   220.     ibis   is.  for   small,   clear 
pieces.      For   large   timbers,   the   increase   in  strength  produced  by 

a  decrease   in  moisture   is   often  entirely  offset  by  checks  and 

> 

Similar  defects  which  develop  during  the   seasoning  process.     Under 
most  conditions   it   is  advisaole  not  to  expect  additional   strength 
due  to  seasoning.      Seasoning  of  beams   increases  the    liability  to 
failure  by  horizontal   shear.        The   curves  shorcn  are  typical.      The 
importance   of  the   fiber- saturation  point   is  evident   from  this 
illustration.      It   occurs  at  about  25$  moisture.     Table   I  opposite 
page   196  was   obtained  from  small  green  sticks  which  were  clear, 
straight  grained,   and  free  from  defects.      In  general,   air  dry 
wood    is  about  50$  stronger  and  kiln  dry  wood   is  about   100$  strong- 
er than  wood   in  the   green  condition.     Re  soaked  -wood   is  not   so 
strong  as  green  wood. 

The  modulus  of  rupture    in  static   bending  and  the  compressive 
strength  parallel  to  the  grain  are   changed  about  4$  by  a  change   of 
1$  in  moisture  content   (when   it   ie  aoout   12$).      For   example,   com- 
pare the  modulus   of   rupture   of  Douglas  Fir   and  Western  Yellow  Pine 
as   given   in  the     table    in  these   notes.      Douglas  Fir  at   9.4$  moisture 
has   a  modulus   of  rupture    of   10,300     Ib.    per   sq.    in.      The  Western 
Yellow  Pine   has   a  moisture   content   of   10.8$  with  a  modulus   of  rup- 
ture   of  9,300   Ib.    per   sq.    in.      To  change  the    latter  to  9.4$ 
moisture  will   increase   the    strength 

(10.3  -  9.4)  x  4  -  5.6$ 

.056  x  9,800  =  550  Ib.  per  sq.  in. 

550  +  9,800  =  10,350  Ib.  per  sq.  in. 


Civil  Engr-8.  Assignment  6.  page  13. 

The  modulus  of  rupture  of  Western  Yellow  pine  at-  9.4$  moisture  is* 
therefore,  about  10,350  Ib.  persq.  in.  For  large  differences  in 
moisture  content  this  4$  difference  iB  strenth  v;ill  not  be  accurate. 
Strength  of  Nails  in  Wood  :~  Read  Articles  246  to  248  inclusive. 
The  holding  force  of  nails,  expressed  in  terms  of  adhesive  strength, 
in  Ib.  per  sq.  in.  of  imbedded  surface  varies  with  the  density  of 
the  wood  and  the  form  of  the  ".nail. 

The  most  recent  tests,  reported  in  Bulletin  No.  1,  "Tests 
on  the  Holding  Power  of  Railroad  Spikes11,  Dy  Beyer  and  Krefeld, 
Department  of  Civil  Engineering,  Columbia  University,  show  that  the 
driving  of  spikes  into  holes,  bored  into  the  tie  to  receive  them, 
reduces  the  crushing  and  bunching  of  the  wood  fibers.   The  pre- 
bored  hole  increases  the  resistance  to  withdrawal  of  the  spike. 
In  soft  woods  the  elastic  limit  of  the  fastening  is  reached  at  very 
small  withdrawals  -  Q.004  to  0.006  inches  -  and  in  oak  the  elastic 
limit  is  somewhat  higher.  A  rail  fastening,  to  approach  permanance, 
must  &t  no  time  be  stressed  beyond  its  elastic  limit  holding  power. 

The  shearing  strength  of  nails,  in  nailed  joints,  varies  with 
the  density  of  the  wood  and  the  size  and  depth  of  penetration  of 
the  nail. 

Working  Stresses :-  Study  Article  249.   Safe  working  stress  for  a 
material  is  the  unit  stress  which,  under  conditions  of  use,  will 
not  cause  structural  damage,  \ior£ing  stresses  must  be  considerably 
below  the  ultimate  strength  of  the  material  for  several  reasons, 
(a)  Where  stressed  to  the  point  of  failure  materials  undergo 


Cvil  Engr-8.  Assignment  6.  Page  14. 

mrked  distortion  and  have  less  stiffness.  These  changes  would 
cuse  unsatisfactory  service  in  the  case  of  a  machine  or  structure. 
( )  The  exact  loading  to  which  a  structure  will  be  suojected  can- 
rt  be  determined.  Actual  conditions  may  vary  considerably  from 
csign  assumptions,   (c)  Structures  are  liable  to  overload  and  some 

,^in  of  safety  nust  be  provided  for  such  contingencies,  (d)  The 
:act  strength  of  the  materials  used  is  never  available,  furthermore 
•he  strength  may  be  affected  Dy  deterioration  or  accidental  damage. 

Where  human  life  is  endangered  by  failure  of  a  structure, 
Drking  stresses  should  be  low.   Under  other  conditions  "where  the 
esults  of  temporary  collapse  are  not  important,  the  use  of  higher 
tresses  are  justified. 

Working  stresses  are  frequently  determined  by  dividing  the 
Itimate  strength  of  the  material,  as  determined  by  actual  test, 
y  a  factor  of  safety.   This  factor  varies  from  2.5  to  as  much  as 
0  for  different  materials  and  different  conditions  of  use.   If  a 
structure  is  designed  with  a  factor  of  safety  of  4,  it  does  not 
aean  that  it  will  fail  at  four  times  the  working  or  design  load, 
forking  stresses  should  be  based  on  and  be  well  below  the  elastic 
limit  of  the  material. 

All  large  timbers,  since  they  have  season  checks,  knots  and 
other  defects  should  not  be  considered  to  be  stronger  than  green 
timber.  "Working  stresses  should  be  based  on  tests  of  green  wood. 
In  the  design  of  wooden  structures  it  should  be  remembered 
that  the  actual  dimensions  of  commercial  lumber  are  usually  less 


Civil  Engr-8. 


Assignment  6, 


Page  15. 


than  the  nominal  dimensions.  Sawed  lumber  is  not  considered  as 
"short"  in  dimensions  unless  an  actual  dimension  is  1/4  inch  or  more 
less  than  nominal.  For  dressed  lumber  (as  lumDer  which  has  been 
planed  is  known) ,an  allowance  of  1/4  inch  for  each  dressed  face  is 
made.   A  12  by  12  inch  stick,  if  dressed  on  four  sides,  would, 
therefore,  actually  measure  about  11  1/2  by  11  1/2  inches. 

Working  stresses  for  structural  timbers  which  pass  the  grad- 
ing rules  proposed  by  the  Forest  Products  Laboratory  are  affected  by 
the  moisture  content.   The  following  table  was  taken  from  recent 
Forest  Service  publications: 
Working  Stresses  permissible  for  Structural  Timbers,  Ib.  per  sq.  in. 


Species 

Bending 

Compression 

Stress  in  extreme 
fiber 

Horizon* 
al  Shear 

//  to  t 

'... 
1 
Wet  .  Out** 

loca-*  side 

tion!  l°ca 
i  tion 

rrain 

1 

In- 
side 
-  loca- 
tion 

J.  t< 

Wet 
loca* 

tion 

3  grain 

Out-J  In- 
side jside 

loca-j  loca- 
tion it  ion 

Wet 

loca- 
tion 

Outside  :.  Inside 
loca-   loca- 
tion   tion 

1  _   4 

Au 

loca- 
tions 

Douglas  Fir 
(No.  1  Struck 
tural) 

1100 

1400 

L    -  «, 

1600 

1 
100 

i 
i 

900  1100 

1200 

225 

250  350 

i 
i   __. 

Douglas  Fir 
(No.  2  Struc- 
tural) 

900 
900 

1100 

1300    90 

- 
800   900 

1000 

200  225  300 

i 

| 

Western  Hem- 
lock 

1100 

1300 

75 

i 
i 

800   900 

750  I  900 

j 

900 
1000 

200 
125 

225  300 

Redwood 

i 

, 
800 

: 

1000 

1200  !   70 

!     l 

' 
160  ;250 

Wet  or  damp  location  -  docks,  piling,  and  sills 

Outside  location  -not  in  contact  with  soil,  bridges,  and 

open  sheds 
Inside  location  -  under  shelter  in  a  dry  location, 

factories  and  wa-rehouses. 


Civil  Engr-8  Assignment  6.  page  16. 

Gracing  rules:-  Read  Article  250.   Structural  timbers  are 
graded  or  classified,  by  inspection,  into  groups  or  grades  so  that 
each  stick  in  a  jiven  group  T.;;ill  have  the  same  value  for  a  certain 
purpose.   Grading  rules  are  generally  prepared  by  timber  producers 
such  as  saw  mill  associations  and  lumber  manufacturers'  associations 
while  timber  specifications,  which  are  written  for  the  purpose  of 
having  timber  that  fulfills  the  requirements  suitable  for  a  definite 
purpose,  are  prepared  bj  the  timoer  user. 

iiany  grading  rules  are  based  on  the  number  and  the  character 
of  defects;  they  have  been  satisfactory  in  classifying  saw  mill 
products  for  wood  v or king  industries  out  they  have  not  been  effective 
in  classifying  timber  in  accordance  v;ith  strength.   The  Forest  Ser- 
vice, the  American  Society  for  Testing  Materials,  and  the  Southern 
Pine  Association  have  adopted  rules  which  provide  for  the  quality 
of  the  wood  as  v;ell  as  limit  the  position,  size,  and  condition  of 
defects. 

Since  the  quality  of  wood  is  indicated  by  the  character  of  the 
annual  rings  as  seen  on  the  cross  section,  and  the  location  and 
size  of  defects,  it  is  possible  to  use  these  factors  in  grading  wood 
as  to  strength.   Durability  is  judged  largely  from  the  proportion 
of  sapvrood  which  is  less  resistant  to  decay  than  heartwood.   Dura- 
bility is  also  affected  by  the  degree  of  seasoning  as  indicated  by 
the  moisture  content. 

Study  Figure  21  on  page  232  and  the  text  paragraph  describ- 
ing it . 


Civil  En^r-8.  ^signment  6.  page   17, 

Laminated  Wood  ;-       Wood,   as  has   been  thoroughly  explained,    is  a 
non-homogeneous  material.      It  has  widely  different  properties   in 
the  various  directions  relative  to  the   grain.     Were  wood  homogeneous, 
with  the   sane    strength  properties   in  all  directions  that   it  has 
parallel  to  the   grain,    it  would  be  unexcelled  for  all  structural 
uses  where,  strength  with  small  weight   is  desired.      Laminated  wood 
approaches  this  desired  condition  in  that   it  produces  equality  of 
tensile   strength  in  two  directions   -  parallel  and   perpendicular  to 
the   board.     Ply.vood      is  the   name  usually  given  to  this  type   of  con- 
struction. 

plywood   Is  made  by  gluing  together   plies   of  wood,   usually  an 
odd   number,    so   laid  that  the  grain  of  alternate   layers   is  approxi- 
mately at  right  angles.      Three-ply  and   five -ply  construction  is 
most  common.      The   -niddle    layer   or  core  with  equal   layers   on  both 
sides  gives  a  construction  that   is   symmetrical  causing  an  equaliza- 
tion of  shrinkage    stresses   so  that  the  wood   should   not  warp.   Warp- 
ing does   occur,   howev<?f. ,     The  causes  are   first,   the  use   of  plain- 
sawed  and  quarter-sawed   lumber   in  the    sa^e  construction  and   second, 
the   combination  of  materials   of  different  moisture  content.     Both 
of  these   factors  can  be   easily  avoided,      feoist are -resistant  coatings 
are   resorted   to   in  order  to  maintain  uniform  moisture  conditions 
in  the  ~;ood.      Plywood    is  used    in  the  manufacture    of  automobiles, 
in  street  and   railway  cars,   and    in  airplanes,   where    light  construc- 
tion  is   required. 

Veneer      is  another  type   of   laminated  wood   construction.      Thin 


Civil  Engr-8.  Assignment  6.  Page   18. 

sheets    of  hard  wood   known  as  veneer  are   glued  to  cheap   lumber  to 
give    it  a  hard  wood   surface.     Veneer   is  cut  by  three   different 
methods.      The   oldest  method    is   sawing,   but  the   saw  kerf  ^vhich  can- 
not be  made  much   less  than  1/20  of  an  inch  wastes  considerable  wood. 
The   second  method   is  known  as  slicing.     Veneer  made  by  this  method 
is  essentially  a  thick  shaving  cut  by  a   large  plane.      The  third 
method   is  called  the   rotary-cut.     A  thin  continuous  sheet   of  veneer 
is  cut   off  the   surface   of  a   log  which  is  rotated   in  a  huge   lathe. 

Sawed  and   sliced  veneer  are   relatively  expensive  and  are 
used  primarily  for   ornamental  and  finish  purposes,      host,  of  the 
veneer  produced  at  the   present  time   is   rotary  cut.     Veneer   is  used 
in  the   manufacture    of  plywood. 

Average   sawed  veneer   sheets  are  from  12  to  16  feet   long, 
usually  not   less  than   1/28   of  an   inch  thick  and   their  v;idth  is 
limited  by  the  diameter   of  the   log. 

Sliced   veneer    is  about   10  feet    long  and    seldom  less  than 
1/16   cf  an  inch  thick   (but  some   species  are   cut   1/100  inch  or   less 
in  thickness)     and  the   diameter   of  the    log  in  width. 

Rotary -cut  veneer    is  about   six  feet   long,    on  an  average, 
with  a  maximum   length  of   16   feet,    some    species  may  be   cut   from 
1/100  inch  to  almost   1/2   inch  in  thickness  and  to  any  width  in 
which  the   material  can  be   handled. 

Mill-Building  Construction :-          One   of  the  uses   of  heavy  timber    is 
in  the   construction  of   large  buildings.      The   marked    success   of  early 
heavy  timber    structures   of  the  ;:iill-construction  type,  which 


Civil  Engr-8.  Assignment  6.  Jfage   IS. 

originated   in  the  New  England   States }    led  to  the   popular  use   of 
this  form  of  construction.      The   term  mill-construction  as  commonly 
used    is   the   name   given  to  that  type      of  building  construction   in 
which  the    interior  framing  and   floors  are   of  timber,   arranged   in 
heavy  solid  masses  with  smooth  flat   surfaces,    so  as  to  expose  the 
least  number   of  corners,   and   to  avoid  concealed   spaces  which  may 
not  be   reached  readily   in  case   of  fire.     AS  usually  designed  the 
walls  are   of  brick   or   concrete,    the   floors  are   of  heavy   plank  laid 
flat  upon   large   girders  which  are   spaced   from  8  to  11  .feet  on 
centers.      These   girders  are    supported    by  wood  posts  or  columns 
spaced   from  16  to  25  feet  apart. 


Civil  Lngr-6.  Questions    co  Assignment,   6.  r^ge   2C. 


1.  Would  a  higher  unit   stress  be  ailowaole   in  a  £iece   of  spruce 
for  a   strut   in  an  airplane  frame   or  a  strut   in  a  large  timber 
bridge?      ~Vftiy? 

2.  What  are  the  most   important  tests  of  wood? 

3.  What   is  the   importance   of  stiffness   in  wood?     Hov:   is   it  measured? 

4.  What   is  the   effect   of  permanent  dead   load   on  the   resistance 
of  wood? 

5.  Explain  why  the  use   of  plain-sawed  and  quarter-sawed  ^ood   in 
the  construction  of  a  piece   of  plywood  will  cause  warping  under 
changes   in  moisture  content. 

6.  Differentiate    oetv-een  grading  rules  and  timber   specifications. 

7.  What  precautions  are  taken  in  the   selection  of  test   specimens? 

8.  Discuss  the  effect   of  moisture   on  the  mechanical  properties 
of  *A' 


9.  Give  the  approximate  ultimate   strengths   of  Douglas  Fir,    in 
the   air-dry  condition,   as  determined  by  the  usual  tests  mads 
by  the  Forest  Products   Laboratory. 

10.  State   the  allov;aole  working  stresses  for  Douglas  Fir  when  used 
in  dry   locations. 


UNIVERSITY   OF   CALIFORNIA  EXTENSION  DIVISION 
Correspondence     Courses    . 

Materials  of  Engineering  Construction 

Civil  Engr.-8  Assignment     7  Prof.    C.  T.  Wiskocil 

BUILDING     STOlfflS 

Uses  and  Production:     Read  Article  251.     As   stated  in  this 
article    stone  has  been  used  asa  building  material    since  the  earliest 
known  times-      It  was  used  principally   in  the   construction  of  walls, 
foundations,  arches,   and  dams.     Many  old   stone  monuments  are   still 
in  a  fair    state  of  preservation.      Stone  and  wood  are  the  only  im- 
portant.   s^ructural  materials  used  in  their  natural    state.     The  use 
of    stone  for    structural  purposes  is  decreasing  because  of  the  de- 
velopment of  reinforced  concrete  for  these  purposes.     Half  a  cen- 
tury ago  building   stone   composed  nearly  the  entire   output  of  the 
quarries*      Some  of  it  was  made   into   lime  but  the  use  of  concrete 
for  foundations,  bridges,    culverts,   curbing,   and  other    structures 
has  reduced  the   demand  for  building   stone  and  lime.      Important 
buildings  in  which  appearance  is  a  large  factor,   are    still  usually 
built  of    stone.     About  70  million  tons  of   stone  are  quarried  an- 
nually in  the  United   States.     The  approximate  value  of  this  output 
is  90  million  dollars.     These  figures  were  taken     from  the  United 
States  Geological   Survey  reports  from  which  the  following  table, 
showing  the  percentage  of  the  entire  output  used  for  different 
purposes,  vas  compiled: 


Engr.-8.     Materials  of  Engineering  Construction.     Assignment  7,  page  2. 

Structural  purposes 

Building  stone  II. Oft 

Paving  blocks  3.0 

Curbing  1.0 

Flagging  0.5 

Rubble  1.0 

Riprap  2.0 

Crushed  stone  38.0 

Monumental  stone  15 «5 

Furnace  flu*  20.0 
Other  uses  8.0 

The   last  item  includes  stone  used  for    such  purposes  as  fur- 
nace  linings,  for  which  refractory   stone  -  dolomite,  quart zite, 
and  mica,   schist  -  is  required,   and  pulverized   stone,  used  by   sugar 
factories,  paper  mills,   glass  works,   alkali  and  other  industrial 
•works. 

Crushed   stone  is  used  for  railroad  ballast,  roads,  and  con- 
crete aggregate. 

In  Article  251,   the  part  of  the  first  paragraph  v/hich  deals     strength 

of  building   stone,    is  important.     It  will  be  noted  that 
rath  the   conditions  which  govern  the    select ion/^is  not   included  in 

these  conditions.     The  corapressive    strength  of   stone  is  nearly  suf- 
ficient to    support    safely,  the  weight  of  the    superimposed  masonry 
and  other   loads  that  come  upon  it.      If  a   stone  had  a  compressive 
strength  of  6,000  Ibs.  per    sq.   in.  and  it  weighed  170  Ibs.  per 
cubic  foot,   it  would  have   to  be  built  into  a  tower  about  5,000  ft. 
high   (6000^   144)  before  the   iciest  block  would  be  brought  to  the 
point  of  failure.     The  Washington  Monument  in  Washington,   D.C.   is 
only  550  ft  high  and  the  Woolworth  Building  in  New  York  City,  with 
its  51    stories,   is  only  792  ft.  high.     These,  to  be   sure,   are  not 
ordinary    structures;    but  it   should  be  remembered  that  there  are 


Engr«.-8.     Materials  of  Engineering  Construction.     Assign.   7,  page  5. 

few   stones  that  have   an  ultimate   compressive    strength  less  than 
6,000   Ibs.   per    cq.    in-     Granites  average  20,000   Ibs.  per    sq«   in., 
while  recently  a  :Tephelite  Basalt  quarried  near  Austin,   Texas  was 
found  to  have  an  ultimate  oompressive    strength  of  53,900   Ibs-  per 
s^»   in.     This  is  an  extreme  case* 

Dead  load,  ho\vever,   is  not  the  only  factor  that  must  be  con- 
sidered  in  the  design  of  masonry    structures*     TJlnd  and  other   live 
loads  r;.ay  cause  a  large  increase   in  the   loading  on  certain  parts 
of  the  foundation •     The   load  in  a  masonry  vra.ll  is  probably  never 
uniformly  distributed  over  the   individual  members  of  the  different 
courses  because  of  uneven  bedding,  and  the    stresses  due  to   loads 
may  be   augmented  by  expansion  and  contraction  of  the   stone,  ex- 
pansion  of  water   in  the  pores  while  freezing,   and  vibration  in 
structures   such  as  bridge  piers-     Furthermore,  the   strength  of 
masonry   is  influenced  by  the   kind  of  mortar  used.     The  highest 
class  of  masonry,    known  as  a shlar ,    laid  in  Portland  cement  mortar, 
is  not   loaded  in  excess  of  500   Ibs.  per    sq.   in.     This  is  well  with- 
in the   compressive    strength  of   stone  used   in  building  construction 
and  the  foregoing   statements   show  the  reason  why   strength  is  not 
considered  in  the    selection  of   stone  for  this  purpose. 

Transportation  charges  effect  the  cost  of   stone  because  of  its 
weight*     A  block  of  granite  2  by  2  by  3  ft.  weighs  a  ton- 
Fashion  also   is  frequently  an   important   consideration  in  the 
employment  of   stone   in  building.      Considerable  demand  for   Califor- 
nia travertine  was  created  in  the   San  Francisco  Bay  region  by  the 


Iingr-8.     Materials  of  Engineering  Construction.     Assign.  7,  page  4. 

use  of  artificial  travertine   in  the  construction  of  buildings  at 
the  Panama-Pacif ic   International  Exposition  at  San  Francisco.     The  use 
of  a  particular  decorative   stone  in  the  construction  of  homes  for 
prominent  people  will  influence  others  in  the    selection  of  a   similar 
building   stone. 

Appearance  and  cost  aside  from  durability  are  the  considera- 
tions given  t/eight  by  the  architect.     There   is  considerable  dif- 
ference  in  the  appearance  of  the  dark  colored,    somber   igneous  rocks 
such  as  diorite  and  gabbro,  and  the   light,  pleasing  colors  of  most 
limestones  and  granites. 

Durability  is  the  most  important  consideration  and  in  the  case 
of  an  untried   stone  its  determination  is  quite  uncertain.     The 
durability  of   stones  in  use,  however,   can  be  raadily  judged  by 
careful  inspection.     Stone  to  be  used  in  steps,  floors  and  other 
pavements,    since   it  is  to  be   subjected  to  abrasion,    should  be  one 
that   shows  greatest  endurance  under    such  conditions.     Frequently 
stone   is  required  to  withstand  the  abrading  action  of  water-borne 
sand,   as  in  bridge  piers,   and  air-blown   sand,   as  in   structures  in 
certain  arid  regions,   and  must  be  tested  for  endurance  under  those 
special  conditions- 

The  ivlineral  Constituents  of  Rocks:  Read  Article  252;  it  is 
of  interest  in  connection  with  the  subject  of  stone  but  it  is  not 
of  such  importance  that  the  details  should  be  remembered. 

Classes  of  Rocks;      Study  Article  253.     Be  able  to  classify 
rocks  according  to  geographical  origin.     Other   classifications  are 


Engr-8.     Materials  of  Engineering  Construction.     Assign.  7,  page   5. 

used]   on  the  basis  of  texture  and   structure,  miner alogical  composi- 
tion,  chemical  composition,   and  geological  age* 

Important  Building  Stone  a:      Study  Article  254  to  260  inclusive. 
Suitable   stones  for   structural  purposes  are  widely  distributed;  the 
principal  classes  include  granite,   limestone,    sandstone,  marble, 
and   slats.     The  follovring  table  gives  the  approximate  production 
of  the  different  classes  of   stone  during  1919.     It  was  prepared 
from  the  U.S.G.S.  report,   "STONE   IN   1919"  by   Loughlin  and  Coons. 

PRODUCTION  IN  THOUSANDS     OF  TONS 
Grai 

Building    stone 

Monumental    stone 

Paving    stone 

Curbing 

Rubble 

Riprap 

Crushed   stone 

Other  uses 

TOTALS, 

It   is  interesting  to  note  that  the  proportion  of  cut   stone  used  for 
structural  purposes  is  only  a   snail   (about  11$)  part  of  the  total 
production.     The  principal  use  for   limestone  is  as  a  flux  in  the 
manufacture  of  pig  iron.     See  Article  580  page  537   in  the  text. 

Granite ;     \Vhile  granite  is  one  of  the  principal  building   stones 
its  greatest    single  use  is  for  crushed   stone*     Vermont  leads  in  the 


Granite 

Basalt   (Trap) 

Lime  stone 

Sandstone 

Marble 

304 

30 

394 

150 

85 

305 

.. 

—  _ 

... 

95 

364 

1 



20 

.w 

50 

«••» 

7 

92 

—  •»• 

98 

80 

328 

92 

IH» 

379 

231 

833 

214 

— 

2,700 

7,053 

21,760 

1,180 

— 

20 

14 

26,400 

790 

153 

4,220 

7,409 

49,722 

2,538 

333 

Engr-8.  Materials  of  Engineering  Construction.  Assign.  7,  page  6. 

production  with  Massachusetts,  Maine,  and  New  Hampshire  closely 
following*  Minnesota  and  Wisconsin  rank  with  the  New  England 
States  in  the  production  of  granite  while  California  leads  the 
We  stern  States. 

Granite  is  quarried  in  about  ten  counties  in  California.  The 
principal  quarry,  which  is  controlled  by  the  Raymond  Granite  Com- 
pany is  at  Krowles,  Madera  County.  About  a  quarter  of  a  million 
cubic  feet  of  stone  have  already  been  removed  from  this  quarry. 

The  stons  is  a  very  fine-grained  light  granite.  Many  important 

in  California 
structure s^have  been  built  vrith  Raymond  granite.  Among  them  are: 

the  Municipal  Auditorium,  the  Post  Office,  the  Sub-Treasury  Build- 
ing, the  Bank  of  California,  and  the  Fairmont  Hotel  in  San  Francisco; 
California  Hall,  the  Doe  Library,  Wheeler  Hall,  Hearst  Mining 
Building,  Boalt  Hail,  Sather  Gate,  and  the  Sather  Tower  of  the  Uni- 
versity of  California  at  Berkeley;  the  Time  Building,  and  Citizens 
National  Bank  Building  in  Los  Angeles. 

Granite  is  an  ideal  building  stone.  It  is  durable  yet  not 
too  hard.  It  is  interesting  to  note  that  in  the  recent  addition 
to  the  Anglo  and  London  Paris  National  Bank  in  San  Francisco,  solid 
granite  columns  were  used.  They  were  4^  ft.  in  diameter  and  22ft. 
long  and  weighed  about  20  tons.  It  took  about  three  months  to 
shape  each  column. 

Lime  stone ;  TiTnile  limestone  is  one  of  the  principal  building 
stones  most  of  the  production  is  used  for  other  purposes.  As  al- 
ready mentioned  it  is  used  for  a  flux  in  the  production  of  pig 


Engr-8.     Materials  of  Engineering   Construction.     Assign.   7,  page  7. 

iron  and  for  various  industrial  uses-      It   is  also  used  in  the  manu- 
facture of  portland  cement    (Article   339,  page   310),   and  in  the 
manufacture  of  lime    (Article  379).     More   limestone  is  pulverized 
and  used  to  improve   soil  than  is  used  for    structural  purposes- 
Limestone   is  also  used  as  a  filler  for  asphalt,  paint,  rubber, 
soap,   and  other  materials.      It  i s  quarried  in  about  20  counties 
in  California.     At  present  the  principal  use  for  this  product  is 
for  macadam  roads  and  concrete  aggregate.     Indiana  leads  in  the 
production  of  limestone  for  building  purposes.     The  best  known 
and  most  7/idely  used  American  limestone  is  the  Bedford  limestone 
which  is  quarried  at  Bedford,   Indiana,   and  Bowling  Green,    Kentucky. 

Marble ;     is  a  crystalline   limestone.     It  is  quarried  in  about 
six  counties  in  California. 

Travertine  is  a  compact  fine-grained  limestone  deposited  on 
the   surface  by  the  water  of   springs  or    streams  holding   lime  in 
solution.     The  Roman  palaces  of  the  period  of  Augustus  were  made 
of  travertine  quarried  at  Tivoli  near  Rome.     A  quarry  at  Fairfield, 
California,    supplies  an  excellent  grade  of  travertine.     The  bench 
.at  the  foot  of  the   Sather  Tower  on  the  campus  of  the  University  of 
California  at  Berkeley  is  made  of  travertine  from  the  Fairfield 
quarry . 

Sandstone :      Sandstone   is  composed  of   sand  grains  cemented 
together  to  form  a   solid  rock.     The    strength  and  durability  de- 
pends upon  the   cementing  material.      Sandstone   is  quarried  in  about 
seven  counties  in  California.     A  large  number  of  the  buildings  at 
Stanford  University  are  built  of    sandstone.     The   St.  Francis  Hotel 


Bngr-8.     Materials  of  Engineering   Construction.     Assign.   7,   page   8. 

and  the  Flood  Building  in  San  Francisco  are  made  of  Colusa   sand- 
stone.    A  large  part  of  the   sandstone  quarried  is  known  as  quartz ite 
(g.anister)  and  is  used  for  making   silica  brick,  for  furnace   lining 
(see  Article  592   on  page  548  of  the  text). 

Trap:     Trap  is  a  designation   (not  used  by  the  geologist)  which 
includes  fine-grained  basic  rocks   such  as  basalt,   diabase,   and  gab- 
bro.     These  rocks  usually  occur   in  columnar   structure  and  present 
a   stepped  appearance.     The   Swedish  word  "trappe"  means  stairs; 
therefore,  trap  has  reference  to  the  occurence  of  the  rock  in  the 
quarry.     Trap   is  tough  and   strong   (stronger  than  granite)  but  it 
does  not  weather  well.      It  is  hard  to  quarry  and  is  used  princi- 
pally for  paving  blocks  and  crushed   stone. 

Slate ;     The  most  valuable  characteristic  of   slate   is  its  ten- 
dency to   split  into  thin   sheets,   leaving   smooth  plane    surfaces- 
Slate   does  not  absorb  water,  posses  considerable  toughness  and 
strength,  and   is  moreover  a  good  insulator  for  electric  current* 
Its   structural  use   is  confined  to  roofing. 

Durability  of   stone :     Read  Articles  261  to  266  inclusive. 
Frost  is  probably  the  most  destructive  agent  for    stone  when  it  is 
exposed  to  the  weather.     Many  varieties  of   stone    show  signs  of  dis- 
intergration  after  a  few  years  of    such  exposure.     The  estimated 
life  of    stone  under  exposure  varies  frcm!2  years  for   soft    sandstone 
to   several  centuries  for  hard  granites.     Study  Article  261   in  the 
text  on  the  weathering  of   stone.     Atmospheric   conditions  affect  the 
durability  of   stone.     The  Egyptian  Obelisk  commonly   known  as 


Engr-8.  Materials  of  Engineering  Construction.  Assign.  7,  page  9. 

Cleopatra's  Needle,  was  built  about  1500  B.C.  '  For  over  3000  years 
it  stood  unharmed  in  the  mild  Egyptian  atmosphere.  "When  it  was 
brought  to  New  York  in  1879,  immediate  steps  had  to  be  taken  to 
save  it  from  the  ravages  of  our  American  climate  by  giving  it  a 
surface  coating.  See  the  third  paragraph  of  Article  262  in  the 
text.  Limestone  and  sandstone  are  not  in  general  very  durable  and 
many  exanples  of  their  rapid  disintegration  might  be  cited.  There 
are,  however,  very  durable  varieties  of  both  these  stones* 

Preservative  coatings  are  effective  in  preventing  the  absorp- 
tion cf  *.-ater  :.nd  protecting  the  surface  of  the  stone  but  they  do 
not  last  long  and  r,ust  be  frequently  renewed. 

Durability  tests  for  stone :  The  most  reliable  test  is  the 
examination  of  exposed  quarry  ledges  or  cut  stone  that  has  been  ex- 
posed to  the  weather.  The  action  of  destructive  agents  may  be 
closely  imitated  in  the  laboratory  but  data  on  the  actual  dura- 
bility are  not  thus  obtained  and  the  interpretation  of  laboratory 
results  is  therefore,  quite  difficult.  The  f reeling  and  thawing 
test,  and  the  acid  test  are  the  principal  laboratory  tests  for 
durability.  The  absorption  test  is  of  value  in  determining  the 
probable  effect  of  weathering.  The  more  water  a  stone  absorbs, 
other  things  being  equal,  the  more  softening  and  harm  will  be  done 
by  atmospheric  acids. 

The  heat  occasioned  by  fires  in  large  buildings  often  exceeds 
150C  decrees  Fahrenheit .  ilo  stofre  will  withstand  this*  Limestone 
is  decomposed  at  about  1200  degrees  Fahrenheit  and  granite  spalls 


Engr-8.  Materials  of  Engineering  Construction.  Assign.  7,  page  10. 

and  cracks  at  these  high  temperatures.  Quenching  intensifies  the 
effects  of  fire.   Clay  products,  brick  and  terra  cotta,  are  superior 
to  stone  in  their  resistance  to  the  effects  of  fire. 

The  Physical  properties  of_  stone :  Read  Articles  267  to  270 
inclusive-  The  coefficient  of  thermal  expansion  is  not  constant 
as  in  the  case  of  metals.  It  increases  with  an  increase  in  tem- 
perature. An  average  value  is  .000004  inches  per  inch  per  degree 
Fahrenheit.  Stone  once  heated  does  not  return  to  its  original  di- 
mensions when  cooled.  This  permanent  expansion  is  mentioned  in 
Article  267;  it  is  important.   Stone  slabs,  particularly  those  of 
marble,  frequently  warp  when  exposed  to  the  weather.   Since  marble 
is  formed  by  a  process  of  slow  deposition,  and  it  is  estimated  that 
the  formation  of  one  inch  took  about  a  thousand  years,  it  is  reason- 
able to  suppose  that  the  stone  is  not  uniform  in  structure  perpen- 
dicular to  its  bedding  plane.  Different  layers  may  have  different 
thermal  properties  which  would  cause  variable  permanent  sets  under 
heating  and  cooling,  sufficient  at  least  to  produce  warping.  The 
surface  of  a  stone  monument  exposed  to  the  direct  rays  of  the  sun 
may  easily  exceed  120  degrees  Fahrenheit.  Marble  slabs  and  shafts 
in  cemetaries  are  frequently  warped.  Recent  tests  show  that  con- 
crete road  slabs  warp,  but  not  permanently,  due  to  differences  in 
temperature  of  the  upper  and  lower  surfaces.  During  the  day  the 
slab  is  concave  downward  and  at  night  when  the  air  is  cooler  than 
the  ground  it  is  concave  upward  so  the  the  edges  are  actually  lifted 
off  the  subgrade. 


Bngr-3.  Materials  of  Engineering  Construction.  Assign.  7,  page  11. 

To  remember  the  approximate  specific  weight  of  stone,  take 
the  weight  of  granite,  about  170  Ibs.  per  cu.  ft.  Trap  rocks  weigh 
more  and  the  other  building  stones  weigh  a  little  less. 

Mechanical  properties  of  stone :   Study  Articles  271  to  273  in- 
clusive. The  strength  of  stone  is  rarely  developed  except  in  lin- 
tels and  top- slabs  for  culverts  where  the  stone  is  used  as  a  beam. 
The  compression  test  is  frequently  the  only  test  made  but  the 
transverse  test,  which  gives  the  modulus  of  rupture  and  the  modulus 
of  elasticity,  is  also  made.  In  your  study  of  a  new  material  make 
a  table  with  average  values  to  compare  it  with  some  material  you 
have  already  examined* 

Average  Ultimate  Strength,  lb.  per  sq.  in. 

Compression         Modulus  of    Modulus  of 


Rupture, 

Elasticity 

Granite 

20,000 

1,500 

8,000,000 

Limestone 

9,000 

1,200 

8,000,000 

Douglas  Fir 
(air   dry) 

Parallel     Perpendicular 

10,000 

1,500,000 

to  the  grain. 

7,000  900 

f 

The  above  values  are  from  tests  on   small  test    specimens.     Re- 
member that  although  average    sandstone   is   stronger  than  average 
limestone,   a  good  limestone   is  stronger  than  a  poor    sandstone. 
Tests  of   stone  are  always  made  on  overn  dry   specimens.      Soaking 
decreases  the    strength  of    stone,  a  fact  which  has  been  noticed  in 
tests  of  marble* 


Engr-o.     Materials  of  Engineering   Construction.     Assign.  7,  page   12. 

Stone,   like  other  brittle  materials  such  as  cast  iron  and  con- 
crete,  does  not  obey  Booke's  lav:.     The   stress-deformation  curves, 
instead  of  being   straight,  to  the  proportional  limit,   are  concave 
upward  -   see  Figures  2,   3,  <.-,   and  5  on  pages  256  and  257   in  the 
text. 

Stone   is  used  in  the  construction  of  various  types  of  roads, 
from  the  block  or  cobblestone  pavements,  to  the  bituminous  macadam, 
cement  concrete,   and  the  water  bound  macadam  pavements.     The 
characteristics  of  the    stone  used  depend  upon  the  type  of  pavement 
and  the  character  of  the  traffic.      In  the  case  of   stone  for  road 
pavements  as  well  as  in  the  case  of  building   stone,  the  crushing 
strength  is  of   secondary   importance,  while  toughness,  hardness  and 
resistance  to  wear  are  of  the  most  importance.     Tests  to  determine 
each  of  these  properties  have  been   standardized  by  the  United  Stated 
Bureau  of  Public  Roads  and  the  American  Society  for  Testing 
Materials.     They  also  publish  requirements  to  guide  in  the   selection 
of  available  material. 

The    specifications  for  crushed   stone  for  concrete  aggregate 
are  rather  general.     They  usually   state  that  any  durable  crushed 
fiftone  or  any  clean,  hard  gravel  not   subject  to  ready  disintegration 
may  be  used. 

Stone  quarrying :     Blocks  of   stone  are  removed  from  the  quarry- 
ledge  by  blasting  or  hand  tools.     Early  Egyptians  cut  grooves  in 
the  rockledge  with  crude  bronze  piclcs.     Dry  wooden  vedges  were 


Engr-3.     Materials  of  Engineering  Construction.     Assign.  7,  page   13. 

pounded  into  the  grooves  and   soaked  with  water.     The  expansive 
force  produced  by  the   swelling  of  the  wood  forced  out  the  block  of 
stone.     Hand  methods  at  the  present  time  require  the  use  of  a 
steel  drill  to  make  a  series  of  holes  in  the  rock  into  which   steel 
wedges  are  driven  to  force  the  rock  apart.     Power  operated  drills 
and  channelers  with  the  use  of  explosives  are  replacing  hand  meth- 
ods*    Power-driven   saws,  planers  and  lathes  are  used  to   shape  the 
blocks  of  rough   stone. 

Stone  ma sonry :     There  are  three  classes  of   stone  masonry  - 
riprap,  rubble  and  cut- stone.     Riprap  is  uncut   stones  piled  up  to 
form  masonry.     It   is  used  for   low  walls  and  to  protect    stream  banks 
from  erosion.     Rubble   is  riprap  with   stones  held  together  with 
mortar*      Cut  or    squared    stones  laid-up  with  mortar  produce  the 
highest  class  of  masonry.     The  term  ashlar  is  applied  to  masonry 
of  the  last  class,  when  the  joints  are  not  more  than  -j=f  inch  thick. 
This  requirement  can  be  met  only  by  having  plane   surfaces  on  in- 
dividual   stones.     This  construction  insures  uniform  distribution 
of  loads,    so  that  the  highest   loads  are  allowed  on  ashlar  masonry. 

The   strength  of  stone  masonry  depends  largely  on  the   strength 
of  the  mortar  used  and  the  thickness  of  the  joints  between  adjacent 
stone  s. 

Riprap  is  not  meant  to  carry  loads.     Rubble  in  lime  mortar 
with  individual   stones  placed  at  random,   is  designed  for  60  Ibs. 
per    sq.   in«,  while  the  allowable   load  on  ashlar  masonry  made  of 
granite   in  port land  cement  mortar  is  600  Ibs-  per    sq.   in. 


Engr-6.     Materials  of  Engineering  Construction.     Assign.  7,  page   14. 

QUESTIONS: 

1.        If  granite  weighs  170  Ibs.  per  cu.  ft.  what  is  its  apparent 
specific  gravity? 

VJhich  beam  Yri.ll   support  the  greatest   load;   one  of  granite  or 
G.  T/ooden  bean  (Douglas  Fir)  of  the   same  dimensions,    span  and  condi- 
tion of   loading? 

3»       Which  of  the  beans  mentioned   in  question  2  will  deflect  the 
most  under  a  given  load?     Why? 

•*•  What  are  the  requirements  for  a  good  building   stone? 

5.  What  are  the  principal  building   stones? 

6.  HOY:  is  the  durability  of    stone  determined? 

7.  What  is  ashlar  masonry?  ^  Jw  ^^ 

8.  What  is  the  allowable   load  on  ashlar  masonry? 

9.  Draw  a  typical   stress-deformation  curve  for    stone. 

10.       How  do  you  account  for  the  v/arping  of  marble    slabs  v/hich  have 
been  exposed  to  the  weather? 


UNIVERSITY   OF   CALIFORNIA  EXTENSION  DIVISION 
Corre  spondence     Cour  se  s 

Materials  of  Engineering  Construction 
Civil  Engr-3  Assignment     8  Prof.   C.  T.  Wiskocil 

STRUCTURAL  GUY  PRODUCTS 

Introduction:     Clay  products  are  widely  used  in  engineering 
construction.     The  material  itself  is  not  used  in  its  natural   state, 
as  stone  and  wood  are  used,   but  is  first  manufactured  into  various 
products.     This  is  a   simple  process  because  moist  clay,  which  is- 
very  plastic,   can  be  molded  into  the  desired  form  and  then  easily 
converted  into  a  stone-like  mass  by  firing  or  burning.     Burnt-clay 
is,  then,  the  actual  material  used  in  engineering  construction. 
It  is  one  of  the  most  durable  materials  as  is  proved  by  the  good 
state  of  preservation  of   specimens  found  in  ancient  ruins.     It 
has  been  used   since  earliest  times.     Clay  pipe  found  on  the   Island 
of  Crete  dates  back,  according  to  one  record,  to  5,000  B.C.     Other 
records  show  that  clay  products  were  used  in  2247  B-C.  and  in  the 
book  of  Genesis  we  read  that  the   Israelites  made  bricks  from  mud 
of  the  river  Nile. 

Brick,  the  principal  clay  product,  has  been  used  for  many  types 
of   structures.     Parts  of  the  Great  Wall  of   China,   211  B.C.,  were 
made  of  brick.     J.  A.   L.  Uaddell  reports  in   "FOLLOWING  THE  GREAT 
WALL  OF   CHINA11    (Engineering  News-Record,    88,   642,  April  20,   1922), 
that  the  bricked  wall  is   still  in  a  fair    state  of  preservation. 
London  was  rebuilt  with  brick  after  the  fire  of  1666  A.D.     The  first 
brick  house   in  America,   built   in  1634  in  Medford,  Massachusetts,  by 


Engr~8»  Materials  of  Engineering  Construction.  Assign.  8,  page  2. 

Gov.  Craddock  of  the  Massachusetts  Bay  Colony,  was  made  with  bricks 
brought  from  Europe.   Independence  Hall,  Philadelphia,  and  the  famous 
old  State  House  of  Boston  were  built  with  brick.  The  first  brick 
pavement  in  the  United  States  was  laid  in  1871  in  Charlestown,  West 
Virginia.  At  Great  Falls,  Montana,  the  Boston  and  Montana  Copper 
Company  erected  what  is  probably  the  tallest  brick  chimney  in  the 
world.   It  is  506  feet  high  and  50  feet  across  the  top. 

Read  Article  274*  Remember  the  classification  of  structural 
clay  products  as  given  in  this  paragraph.  Clay  suitable  for  the 
manufacture  of  ordinary  building  brick  occurs  in  large  deposits  in 


many  leoa*r3ren-»»  Special  grades  of  clay  are  required  for  the 
making  of  paving  brick,  fire  bricks,  terra  cotta,  and  chemical 
stoneware  • 

The  following  table  gives  the  approximate  distribution  of  the 
clay  products  made  in  the  United  States: 

product  Percentage  of 

Total  Production 

Common  brick  20 

Fire  brick  18 

Sewer  pipe  8 

Hollow  tile  6 

Drain  tile  5 

Paving  brick  5 

Face  brick  4 

Tile  (not  drain)  3 

Arch.  Terra  Cotta  3 

Other  products  5 

Pottery  23 

Ravr  materials  used  in  the  manufacture  of_  clay  products:  Study 
Articles  275  and  276;  they  describe  the  various  classes  of  clays  in 
common  use  and  give  the  composition  of  clays,  notice  that  clay, 


Engr-6.     Materials  of  Engineering   Construction.     Assign.    8,  page   3» 

shale j    and    slate  differ   only   in  degree  of  consolidation   and  that 
the  principal  elenents  are    silica,   alumina  and  iron  oxide. 

Pure   clay   is  hydrated  aluminum   silicate    (kaolin)   and  is  pure 
•white.      It   is  produced  by   the  -weathering  of  pure  feldspar,   a  group 
of  mineral   substances  consisting  of   silicates  of  alumina,  potash, 
soda  and  lime*     Potash  feldspar   is  known  as  orthoclase. 

Common  clays  are  formed  by  the  weathering  of  igneous  rocks 
and  clayey   limestones.     They  contain  iron  oxide,   lime  and  magnesia. 

Che^iical  action  is  not  necessary  in  the  di sintergration  of 
rocks;  weathering  cashes  out    some  of  the    silica,   as  in  the  case  of 
the  weathering  of  feldspars. 

Soda,  potash,    lime,  magnesia,    and  ferrous  oxide   combine  with 
silica  and  form  fusible  compounds  which  act  as  fluxes.      If  they 
are  absent  the  burnt  clay   is  porous.      If  they  are  present  in   suf- 
ficient quantities,   the  granules  of  clay  are  fused  and  a  vitrified 
product   is  formed. 

Article  275  divides  clays  according  to  the  geological  manner 
of  formation  into  residual,    sedimentary  and  glacial  clays.     All 
classes  are  used  for   brick  making  but  the    sedimentary  clays  are 
most  frequently  found    satisfactory.      Sedimentary   clays  may  be 
marine   clays.,    lacustrine,   flood-plain,   or  estuarine   clays.     The 
marine   clays  yield  the   most    satisfactory  material  for  the  manufacture 
of  brick.      In  tais  class  are  the  white-burning   clays  -  ball   clays 
and  kaolins  -  also  fire   clays  and   impure   clays  and    shales. 


Engr-8.     Materials  of  Engineering   Construction.     Assign.   8,   page  4. 

The  I'ollo.ving  table  gives  a  typical  distribution  of  clays   sold 
annually   in  the  United  States.     The  figures  are   in  tons.     The   clays 
sold  are  estimated  to  be  only  a   small  proportion  of  the  total 
amount  mined.     The  table   is  interesting,  nevertheless,    since   it 
gives  the  commercial  names  of  the  various  clays  and    shows  the  uses 
to  v:hich  clay   is  put  other  than  for    structural  purposes. 

Kxolin 
Paper   clay 
Slip   clay 
Ball  clay 
Fire   clay 
Stoneware   clay 
Brick  clay 
Miscellaneous 

Clay  available  for  the  manufacture  of  clay  products  is  one  of 
the  most  widely  distributed  minerals.     Hence  there  are  clay-working 
plants  in  every   State   in  the  United  States.     The  manufacturers  who 
use   low-grade  clays  usually  mine  their  own  raw  material  but  the 
percentage  of  manufacturers  mining  their  own  clay  decreases  as  the 
use  of  a  higher-grade   clay  is  employed.     Nearly  every  manufacturer 
who  makes  the  highest-grade  ware  buys  the  clay  he  uses. 

Kaolin,  the  purest  form  of  clay,    is  produced  principally  in 
the   Southern  States.      It   is  used  mostly  in  the  manufacture  of 
china,   white  ware,    such  as   semiporcelain,    and    semivitreous  porce- 
lain ware.      Some   is  used  also   for   fire  brick  and   in  the  manufacture 
of  paper. 

Paper   clay,   as  the  name   indicates,   is  used  principally   in  the 
paper  mills  for   a  filler  and  coating  for  paper.     A  largo  part  of 
this  clay   sold   is  used  for   the  purposes   listed  under   kaolin,   and 


Engr-8.  Materials  of  Engineering  Construction.  Assign.  8,  page  5. 

also  in  the  production  of  pottery  and  tile.  About  six  percent  of 
the  paper  clay  sold  is  used  by  the  cement  mills  in  the  manufacture 
of  white  cement.  This  clay  is  also  used  in  the  manufacture  of  oil 
cloth  and  phonograph  records  and  paint  filler  and  pigment.  Georgia, 
North  Carolina,  and  Illinois  are  the  principal  producers  of  paper 
clay. 

Slip  clay  is  an  easily  fusible  material.  Its  chief  use  is  in 
the  manufacture  of  artificial  abrasives,  such  as  emery  wheels,  and 
for  glazing.  Slips  are  applied  to  architectural  terra  cotta  and 
pottery  to  give  the  product  an  impervious  surface.  Ohio  and 
Michigan  are  the  principal  producers  of  slip  clay. 

The  principal  use  for  ball  clay,  which  is  a  plastic  white- 
burning  clay,  is  for  white-ware,  such  as  high-grade  pottery  and 
tile,  porcelain  electrical  supplies  and  sanitary  ware.  Most  of  the 
supply  comes  from  Tennessee  and  Kentucky. 

Fire  clay  finds  its  greatest  use  in  the  manufacture  of  re- 
factory  products.  It  is  used  for  fire  brick,  converter  and  cupola 
linings  (in  the  steel  industry),  and  in  the  manufacture  of  terra 
cotta.  These  are  hov/ever,  only  the  principal  uses;  there  are 
many  others.  This  type  of  clay  is  probably  used  for  more  dif- 
ferent purposes  than  any  other.  It  is  mined  in  32  states,  Penn- 
sylvania and  Missouri  producing  the  greatest  amounts.  See  the 
note  on  fire-clay  in  Article  275  in  the  text. 

Stoneware  clay  is  refactory  or  semirefractory  and  is  used 
chiefly  in  the  manufacture  of  stoneware  and  chemical  stoneware. 


Engr-8.  Materials  of  'Engineering  Construction.  Assign.  8,  page  6. 

Lover -grade  clays  are  used  in  the  manufacture  of  building  and 
paving  brick,  drain  tile,  sewer  pipe,  and  fireproof ing.  Almost  all 
of  the  manufacturers  of  these  products  mine  their  own  clay. 

Read  Article  277  carefully.  It  gives  the  physical  properties 
of  raw  clay  and  the  relation  of  these -properties  to  those  of  the 
burnt -product.  Plasticity  is  an  important  physical  property.  The 
necessity  for  a  certain  degree  of  plasticity  is  evident  to  anyone 
•who  has  ever  attempted  to  work  wetted  clay*  Most  of  us  are  not 
familiar  with  clay  working  methods;  yet  even  those  who  are  have 
often  wondered  therein  the  hardship  for  the  Israelites  lay  when 
they  were  forced  by  Pharoah's  taskmasters,  according  to  the  Bible 
story,  to  make  bricks  without  straw.  Some  have  thought  that  the 
straw  was  added  to  the  clay  as  a  binder  just  as  hair  is  added  to 
plaster;  but  because  of  the  weakness  of  the  straw  fiber  this  is 
not  an  adequate  explanation-  No  more  satisfactory  explanation  was 
offered  until  Dr.  E«  C-.  Ache  son,  the  discoverer  of  carborundum, 
found  in  his  experiments  that  the  plasticity  of  clay  was  increased 
by  additions  of  dilute  solutions  of  tannic  acid.  Moreover  the 
strength  of  the  dried  clay  was  greatly  increased.  Although  straw 
does  not  contain  tannic  acid  it  was  found  that  the  water-extract 
of  straw  was  just  as  effective  as  were  solutions  of  tannic  in  in- 
creasing the  plasticity  and  strength  of  clay. 

Excessive  shrinkage  of  clay  is  undesirable,  but  a  small  amount, 
about  Q%,  aids  in  making  a  more  compact  material. 


Engr-8.     Materials  of  Engineering   Construction.     Assign.   8,  page  7. 

Manufr.ctv.re  of  clay  products:     The  method 'of  manufacture   is 
approximately  the    same  for  all   classes  of  clay  products.      Study  the 
steps  in  the  process  as  given  in  detail  in  Articles £78  to  286 
inc  lv,  sive  • 

Any  clay  which  possesses  a   sufficient  plasticity  for  molding 
and  which  will  burn  to  the  proper  hardness  is  used  in  the  manufacture 
of  bricks-     Usually  impure  clays  are  employed  and  they  require    special 
treatment  as  described  in  Article  278. 

The  molding  processes  are  described  in  Article  279.     A  small 
proportion  of  common  brick  is  still  made  by  hand  methods*     There 
are  two  methods  of  hand  molding,    slop-molding  and   sand-molding. 
In  the  former,  water  is  used  to  prevent  the  clay  from  adhering  to 
to  the  mold  and  in  the   latter  method  the    same  result  is  accomplished 
by  the  use  of    sand.     Eond  made  brick  is  the  lowest  grade  of  brick. 
Machine-made  brick  is  made  by  three  methods,    soft-mud,    stiff -mud, 
and  dry-press.     The  process  used  depends  upon  the  characteristics 
of  the   clay  employed  and  the   class  and  quality  of  brick  desired. 

Artificial  methods  of  drying  clay  products,  as  described  in 
Article  280  are  coming  into  general  use   in  the  manufacture  of  brick. 
Higher  gro.de  products  are   seldom  dried  any  other  way. 

The  two  classes  of   kilns,   the   intermittent  and  continuous,   are 
described  in  Article  281.     The   intermittent   kiln  consists  of  tr/o 
types,  the  up -draught  and  down-dr  aught   kilns*     The  doT;n- draught 
principle   is  used   in  the   continuous  kiln.     The  old    scove   kiln, 
which  is  essentially  an  up-draught   kiln,   is  still  common  in   small 


Engr-8.  Materials  of  Engineering  Construction.  Assign.  8,  page  8. 

yards  where  the  hand  process  of  molding  brick  is  used.  The  down- 
draught  kiln  is  more  efficient  than  the  up-draught;  and  it  burns 
very  evenly  terra  cotta  and  pottery,  as  well  as  brick.  The  con- 
tinuous type  of  kiln  is  more  economical  than  any  other  but  it  is 
more  expensive  to  install. 

The  heating  of  clay,  \vhich  is  necessary  to  give  it  its  maximum 
strength  and  hardness,  is  known  as  firing  or  burning.  The  process 
is  described  in  detail  in  Article  282.  The  firing  of  a  scove  kiln 
usually  takes  about  &.  week* 

Read  Article  233;   It  will  be  referred  to  when  terra  cotta 
and  sewer  pipe  are  discussed. 

The  degree  of  burning  of  light-colored  ware*  in  a  normally 
operated  kiln,  can  be  quite  accurately  estimated  by  the  color  of 
the  product  if  the  characteristics  of  the  clay  ate  known.  Flashing, 
however,  (see  Article  285)  makes  it  difficult  to  judge  the  degree 
of  burning  by  means  of  the  final  color  of  the  waVe. 

Annealing  is  of  highest  importance  in  the  manufacture  of  all 
clay  products.  After  the  ware  has  been  properly  burned  the  tem- 
perature of  the  kiln  is  reduced  at  a  slow,  uniform  rate  until  that 
of  the  surrounding  astmo sphere  is  reached;  the  ware  is  then  removed. 

When  the  ware  is  removed  from  the  kiln  it  is  sorted  according 
to  quality,  which  is  determined  by  the  degree  of  burning,  and  the 
freedom  from  such  imperfections  as  excessive  warping,  cracks,  and 
deep  kiln-marks.  There  is  a  special  market  for  inferior  products. 


Engr-8.     Materials  of  Engineering  Construction.     Assign.   8,  page  9. 

Tests  of    structural  clay  products:      Study 'Articles  287  to  296 
inclusive  and  read  Appendix  A,  pages  807  to  814   inclusive.     Be  able 
to  list  the  two  classes  of  tests,   those  made  en  the  job  and  those 
made  in  the   laboratory. 

Examination  of  appearance   in  the   strict   sense  is  not  a  test, 
it   is  visual  inspection.     Intelligent  physical  inspection,  with 
the  hammer  and  hardness  tests,   are  often   sufficient  to  determine 
the  acceptability  of   structural  clay  products.     In  order  to  de- 
termine mechanical  properties  and  the  effect  of  changes  in  materials 
or  methods  of  manufacture   it  is  necessary  to  have  more  elaborate 
tests  made.     The  transverse  test,  described  in  Article  300,   is  the 
most   important  test  made  on  building  brick.      It  is  also  used  for 
paving  brick.     The  compression  tests  are  made  on  brick  of  all  kinds 
anc5.  on  various  other  clay  products  such  as  hollow  building  tile  and 
clay  pipe.     The  methods  for  making  the  pipe  tests  are    shown  in 
Article  293.      In  addition  to  these  tests,  pipe   is  also  tested  for 
its  resistance  to   internal  pressure*     Single  lengths,   and  often 
several   lengths  put  together;  are    subjected  to  hydrostatic  pressure. 
The  rattler  test  described  in  detail   in  Appendix  A  is  still  the 
standard  abrasion  test  for  paving  bricks.     Tests  of  this  character 
are   intended  to   imitate  the  conditions  under  vhich  the  product   is 
to  be  used.      In   spite  of  the  fact  that  the  rattler  test  does  not 
fulfil  these  requirements  it  has  been  in  use  for    some  time.     The 
test  described   in  Article  295  has  never  been   standardized  and  ac- 
cepted by  the  American  Society  for  Testing  Materials.      In  all 


Engr-8.  Materials  of  Engineering  Construction.  Assign.  8,  page  10. 

testing,  as  described  in  the  case  of  the  alternate  freeing  and  thaw, 
ing  test  in  Article  293,  the  conditions  of  actual  testing  should 
be  standardized  so  that  the  results  of  different  laboratories  and 
tests  made  at  different  times  will  be  comparable*  Differences  in 
the  shape  and  size  of  the  test  specimen,  rate  and  manner  of  apply- 
ing the  load  and  method  of  general  procedure  all  affect  the  results 
of  the  test. 

Building  Brick;  Read  the  text,  Articles  297  to  303  inclusive, 
on  the  subject  of  building  brick. 

The  manufacture  of  clay  products  has  already  been  described, 
and  specific  information  on  brick  has  been  given.  Article  297 
emphasizes  some  statements  previously  riade.  Bricks  after  being 
molded  are  dried  for  a  period  varying  from  several  hours  to  several 
days  depending  upon  the  method  of  molding  and  drying.  After  dry- 
ing they  are  burned  in  a  kiln  for  about  a  week,  the  temperature  of 
the  bricks  being  very  gradually  raised.  The  cooling  process  takes 
place  gradually  over  a  period  of  several  days. 

Brick  may  be  classified,  as  stated  in  Article  298,  according 
to  method  of  molding,  degree  of  burning,  form  and  use.  In  general 
all  bricks  have  the  same  proportions:  the  width  of  two  bricks 
plus  a  mortar  joint  will  equal  the  length.  When  used  in  the  facing 
of  masonry,  bricks  must  have  true  surfaces  and  sharp  edges.  Face 
bricks  c.re  pressed  or  repressed  before  firing  in  order  to  insure 
these  necessary  qualities.  Glazed  brick  are  made  by  coating  one 
side  of  the  unburned  common  brick  with  a  slip  cloy  of  the  desired 
color  over  which  a  second  cor.t  of  transparent  glaze  is  applied. 


Engr-6.  Materials  of  Engineering  Construction.  Assign  8,  page  11. 

These  coatings  fuse  into  the  brick  in  the  burning  process.  Enameled 
brick  are  made  of  a  higher -grade  clay.  In  the  burning  it  fuses  and 
unites  with  the  body  of  the  brick*  The  enamel,  which  usually 
contains  an  oxide  of  tin  is  applied  to  the  unburned  *or  to  the 
finished  brick.  Glazed  and  enameled  bricks  are  used  for  build- 
ing courts  and  interior  finish.  Tapestry  brick,  the  peculiar  sur- 
face cf  which  is  formed  by  cutting  off  a  thin  slice  by  a  wire,  is 
also  used  as  a  face  brick. 

Study  the  requirements  of  good  building  brick  listed  in 
Article  299.  This  is  an  important  article.  The  first  paragraph 
in  this  article  mentions  efflorescence.  It  is  a  surface  dis- 
coloration, usually  white,  but  occasionally  green  or  yellow, 
formed  by  the  leaching  out  of  soluble  salts  from  the  interior 
of  the  brick,  and  the  depositing  of  these  on  the  surface  by  the 
evaporation  of  the  v.rator.  Besides  being  unsightly  this  process  is 
liable  to  disintegrate  the  brick.  Efflorescence  can  be  prevented 
by  using  water  and  clay  free  from  the  soluble  salts  of  magnesium, 
sodium,  and  potassium.  If  this  cannot  be  done,  an  effective  method 
of  prevention  is  the  preliminary  treatment  of  the  raw  materials 
with  barium  salts  to  convert  the  soluble  salts,  which  usually  exist 
as  sulphates,  into  the  insoluble  barium  sulphate.  Careful,  rapid 
drying  of  the  molded  brick  to  prevent  the  salts  fron  coming  near 
to  the  surface  and  hard  burning  to  volatilize  the  alkalies  and  to 
mnke  r.  dense  brick  both  help  to  prevent  efflorescence.  After  the 
brick  are  in  place  efflorescence  can  be  prevented  only  by  keeping 


Engr-S.  Materials  of  Engineering  Construction.  Assign,  8,  page  12 

the  brick  dry.  Defective  drain-spouts  often  saturate  the  surround- 
ing brick;  the  source  of  water  should  be  removed,  as  efflorescence 
is  likely  to  result.  Brick  can  be  kept  dry  by  surface  coatings 
of  waterproofing  material  such  as  paraffin. 

Tests  of  brick  are  given  in  Article  300,  •  Look  over  the  tables 
given  on  pages  282  and  283;  note  the  variation  for  the  same  class 
of  bricks.  Determine  average  values  to  compare  with  similar  data 
already  obtained  for  the  materials  you  have  studied*  Take  good 
building  brick;  assign  an  average  compressive  strength  of  4,000 
Ibs.  per  sq.  in.,  an  average  modulus  of  rupture  of  1000  Ibs,  per 
sq.  in,  and  an  average  modulus  of  elasticity  of  6  million  Ibs,  per 
sq,  in.  The  strength  of  brick  masonry,  just  as  in  the  case  of 
stone  masonry,  is  much  less  than  the  strength  of  its  component 
parts.  The  compress ive  and  tensile  strength  of  individual  brifeks 
is  of  relative  value  in  the  comparison  of  different  kinds  of 
brick*  The  fractured  surface  of  the  brick  in  the  transverse  test 
affords  an  opportunity  to  observe  the  texture  and  uniformity  of 
structure.  The  stress-deformation  curves  are  similar  to  those  of 
cast  iron  and  concrete  -  also  briille  materials  -  and  usually  are 
not  as  straight  as  indicated  in  Figure  6  on  page  284,  The  modulus 
of  elasticity,  therefore,  is  not  uniform  but  decreases  with  in- 
creasing loads. 

Brick  Masonry :  At  the  time  brick  was  made  by  hand  (the  first 
power-operated  machinery  being  used  about  1840),  stone  made  the 
highest-grade  masonry.  At  present,  however,  with  a  large  variety 


Engr-8.  Materials  of  Engineering  Construction*  Assign.  8,  page  13, 

of  high-grade  bricks  available,  brick  masonry  compares  irell  vrith 
the  best  gro.de  of  stone  masonry.  Well  made  masonry  of  good  brick 
is  as  nearly  permanent  as  any  structural  material.  Brick  masonry 
is  more  resistant  to  fire,  more  easily  built,  and  usually  cheaper 
than  ston3  masonry. 

Mortar  is  an  important  factor  in  the  construction  of  masonry. 
Its  principal  function  is  to  form  a  bedment  ar.d  to  hold  the  bricks 
together.  The  influence  of  the  joint  upon  the  color  of  the  brick- 
v/ork  can  be  understood  rrhen  consideration  is  given  to  the  fact  that 
the  :nortar  joint  constitutes  from  1/10  to  1/5  of  the  surface  of  the 
finished  •wall.  The  mortar  also  adds  effectiveness  to  the  appear- 
ance of  the  bond,  vrhich  is  the  torn  used  for  the  brickwork  patterns 
or  relative  position  of  the  faces  and  heads  of  the  bricks  as  laid. 
!  lor  tar  is  made  of  lime  and  sand,  cement  and  sand,  or  a  combination 
of  lime,  cenent,  and  sand. 

1.   The  kind  of  nortar  has  an  important  effect  upon  the 
strength  of  brick  masonry.  2.  Lime  mortar  is  not  as  strong  as 
cement  mortar.  3.  The  strength  of  masonry  is  proportional  to  the 
transverse  strength  of  the  bricks  used  in  its  construction,  llortar 
joints  should  be  as  thin  as  possible  and  of  uniform  thickness. 
Regularity  in  the  shape  of  the  bricks  is  essential.  4.  Since  the 
initial  failure  of  brick  masonry  is  caused  by  a  transverse  failure 
of  individual  bricks  the  ultimate  strength  of  this  type  of  con- 
struction can  be  increased  by  laying  the  bricks  on  edge  instead 
of  flat  or  by  using  bricks  of  more  than  ordinary  thickness. 


Engr-6.  Materials  of  Engineering  Construction.  Assign.  8,  page  14. 

£and  Lime  Brick;   Study  Articles  304  to  307  inclusive.  A  sand 
lir.e  brick  is  not  a  burnt  clay  product  but  it  is  used  for  the  same 
purposes  and  has  the  sane  size  and  shape  as  a  clay  brick.  The 
sand-lime  brick  consists  of  about  90$  sand  and  10$  line.  About 
&5fo  of  the  sand  is  retained  on  a  100-mesh  sieve  and  constitutes 
the  aggregates,  ivhich  are  bound  together  by  a  calcium-silicate. 
This  binding  material  is  formed  by  a  chemical  combination  of  the 
lime  and  part  of  the  sand  Tvhich  passes  the  100-mesh  sieve. 

The  bricks  have  fairly  high  strength  when  they  are  removed 
from  the  hardening  cylinder  and  it  increases  for  some  months  after 
they  have  been  made.  Their  ultimate  strength  is  about  three-fourths 
that  of  good  building  brick. 

Paving  Brick:   Study  Articles  308  to  310  inclusive.  Paving 
bricks  differ  from  building  bricks  in  several  -ways.  The  selection 
of  suitable  clay  is  more  limited,  shale  being  usually  employed. 
The  burning  tempera.ture  is  higher  because  it  is  necessary  to  bring 
the  clay  to  the  point  of  actual  vitrification  so  as  to  secure  the 
proper  hardness  in  the  finished  brick.  The  prevailing  size  of 
paving  bricks  is  3  by  4  by  8-1/2  inches.  For  maximum  toughness 
the  annealing  period  should  be  about  10  days  as  stated  in  Article 
285.  Only  the  properly  vitrified  bricks  make  satisfactory  paving 
material;  the  overturned  bricks  are  used  for  foundations  and  for 
sewer  construction  vrhile  the  underburned  bricks  make  and  excel- 
lent building  brickc  Average  values  for  compressive  strength  are 
10,000  Ibs.  per  sq.  in.;  for  transverse  strength  use  2,000  Ibs. 


Engr-8.  Materials  of  Engineering  Construction.  Assign.  8,  page  15. 

per  sq,  in.  and  6,000,000  Ibs.  per  so.  in.  for  the  modulus  of  elas- 
ticity. Remember  that  the  maximum  permissible  loss  in  the  rattler 
test  is  28$,  and  that  the  bricks  must  be  dry  when  tested.  The 
abrasion  loss  of  wet  bricks  or  bricks  saturated  Tilth  bituminous 
materials  is  greatly  reduced. 

Refacwory  Brick:  Study  Articles  311  to  315  inclusive,  Re- 
factory  bricks  are  capable  of  withstanding  the  effects  of  high  tem- 
p3ratures.  There  ere  three  classes  of  refr.ctory  bricks:  acid, 
basic,  and  neutral.  All  are  burned  at  a  high  temperature.  The 
principal  use  of  these  bricks  is  in  the  steel  industry  where  the 
type  of  brick  selected  depends  upon  the  process  of  steel  manufacture, 
whether  acid,  basic  or  neutral. 

Ho  11 ow  Building  Blocks:  Study  Article  316.  These  blocks, 
which  are  often  referred  to  as  hollow  tile,  develop  their  greatest 
strength  when  laid  on  end.  The  material  resembles  ordinary  hax*d 
burned  brick.  The  average  compressive  strength  of  well  burned  tiles 
is  7, COO  Ib.  per  sq.  in.  with  a  modulus  of  elasticity  of  about 
4,000,000  Ib.  per  sq.  in.  The  strength  of  light-burned  tiles  is 
about  30?£  lower. 

Head  Article  317  on  the  strength  of  hollow  tile  columns;  it 
is  not  very  important. 

Read  Articles  318,  33.9  and  320  on  roofing  tile,  c.nd  floor  and 
wall  tils.  Roofing  tile  is  usually  made  of  terra  cotta  and  burned 
at  a  high  temperature  to  insure  hardness  and  low  absorption.  Tile 
makes  a  very  durable  but  rather  heavy  roofing  mr.terir.l. 


Engr-8.  Materials  of  Engineering  Construction.  Assign*  8,  page  16. 

Terra  Cotta.:  Read  Articles  321  and  322.  Terra  cotta  lumber 
is  not  extensively  used.  Architectural  terra  cotta,  however,  is 
one  of  the  standard  building  materials.  Permanent  buildings  faced 
vrith  terra  cotta  are  made  in  the  United  States,  Australia,  Japan, 
and  South  America  and  the  material  is  'not  thought  of  as  a  substitute 
or  an  imitation  of  stone.  Terra  cotta  requires  considerable  strength 
and  accuracy  in  the  finished  -.rare,  therefore,  clays  of  appropriate 
composition  are  limited  and  nust  be  carefully  selected.  Clays  form- 
ing the  body  of  the  vrr.re  are  nixed  for  "both  chemical  and  mechanical 
reasons.  Plaster  of  Pr.ris  molds  are  taken  fror.  plaster  of  Paris 
models  *  These  molds  have  to  be  specially  made  to  provide  for  the 
shrinkage  that  normally  occurs  in  drying  and  burning.  A  mold  with- 
stands the  -;;er.r  of  from  20  to  50  pressings  according  to  size*  In 
the  pressing  shop  the  molds  are  faced  v;rbh  from  1  to  2  inches  of 


6      £ 

and  partitions  about  1  inch  in  thickness*  leavwsk§  spaces  or 


cells  of  about  six  inches^  The  partitions  are  built  up  to  rein- 
force and  strengthen  the  unit.  The  piece  is  then  turned  out  on 
the  drying  boards  "There  it  is  retouched,  After  drying,  the  piece 
passes  before  the  sprayers  vrtiere  the  surface  glaze,  /finish,  slip, 
•or  color  is  applied  "by  an  atomizer  vrith  compressed  air.  In  burn- 
ing, the  ware  is  piled  in  muffle  kilns  on  fire-brick  posts  and  .  * 
slabs  so  that  each  piece  is  free  from  r.ny  extra  weight.  The  burning 
temperature  is  about  2,200  degrees  Fahrenheit. 

Almost  any  color  tone  can  be  had  in  terra  cotta,  from,  the 
pure  rrhito  through  the  crean  coid  buff  shades  into  the  greys.  The 
texture  ranges  from  the  natural  clay  and  the  smooth  or  honed 


Engr-8.  Materials  of  Engineering  Construction.  Assign.  8,  page  17. 

finish  through  different  degrees  of  tooling,  dragging,  and  stippling 
to  any  degree  of  desired  roughness.  The  surface  is  made  impervious 
with  a  slip,  varying  through  matt  or  dull  to  lustrous  and  brilliant 
glazes.  The  use  of  color  or  polychrome  in  terra  cotta  is  being  ap- 
plied to  both  interior  and  exterior  decoration. 

There  are  many  examples  of  the  use  of  terra  cotta  in  building 
construction  in  California.  The  Fireman's  Fund  Insurance  Building 
in  San  Francisco  and  the  Yolo  County  Courthouse  in  Woodland  are 
particularly  good  ones.  Others  are  the  Golden  Gate  Valley  Branch 
of  the  San  Francisco  Public  Library,  the  Hobart  Building  and  the 
trim  on  the  Southern  Pacific  Building  in  San  Francisco;  the  Bank 
of  Italy  in  Fresno;  the  Northern  California  Bank  of  Savings  in 
Harysville;  the  First  National  Bank  in  Santa  !!aria;  and  the 
Farmers  and  Merchants  National  Bank  in  Stockton.  Then  there  are 
notable  examples  in  buildings  in  the  large  cities  in  the  United 
States;  such  as  the  Woolworth  Building,  the  Hudson  Terminal 
Buildings,  the  Produce  Exchange  and  the  r'orld  Building  in  New  York 
City.  Terra  cotta  is  well  adapted  to  interior  facings,  as  is  shown 
in  the  United  States  Post  Office  at  Pasadena,  California. 

Study  Articles  323,  324  and  325  on  sever  pipe,  drain  tile, 
and  conduit.  Sewer  pipe  is  usually  made  with  socket  ends,  referred 
to  is  bell  ends  in  the  text,  and  the  joints  are  made  tight  by  the 
use  of  cement  mortar.  Sewer  pipes,  while  often  spoken  of  as  vit- 
rified pipes,  are  not  actually  vitrified.  The  salt-glaze .general- 
ly used  gives  them  the  appearance  of  a  vitrified  product.  Common 
salt  (sodiurt  chloride)  is  thrown  on  the  kiln  fires.  It  volatilizes 


Materials  of  Engineering  Construction.  Assign.  8,  page  18 

and  the  sodium  vapors  react  with  the  clay  and  form  a  fusible 
sodium-aluminum-si  lie  ato  which  covers  the  surface  with  a  glaze. 
This  glase  is  very  thin  and  is  not  as  effective  as  vitrification 
in  reducing  "Sweating"  of  pipes  under  hydrostatic  pressure  tests. 
Salt  glazed  pipe  is  much  cheaper  than  a  vitrified  pipe  would  be. 
There  is  considerable  loss  in  the  manufacture  of  this  product  be- 
cause cf  warping  and  distortion  in  the  drying  and  .firing  processes. 

Drain  tile  is  a  cheaper  product.  It  is  fired  at  a  lower 
temperature  and  is  not  very  dense.  No  r.ttenpt  is  made  to  nake  the 
material  porous  because  the  water  enters  the  pipe  through  the 
joints  and  not  through  the  walls  of  the  pipe. 


—  >:<  - 


QUESTIONS: 

1.  Classify  clays  according  to  geological  formation. 

2.  TJfhat  can  be  considered  a  good  brick? 

3.  Could  a  brick  be  satisfactory  for  one  purpose  and  unsuited 
for  another? 

4.  What  bricks  are  made  in  your  locality?  which  are  preferred 
and  why? 

5.  How  does  sewer  pipe  differ  from  drain  tile? 

6«i   How  are  sand-lime  bricks  made? 

/^ 

7.  '.That  is  efflorescence?  Can  it  bo  prevented? 

8.  HOT;  is  architectural  terra  cotta  madey 

9.  Give  the  average  compressive  strength,  transverse  strength, 
and  modulus  of  elasticity  of  building  bricks  r.nd  paving  bricks. 

10.   How  does  the  strength  of  brick  masonry  compare  with  that  of 
the  individual  brick  used  in  its  construction? 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 
Civil  Engr-S.A.          Assignment  9.   Professor  C.  T.  Y/iskocil 

PORTLAND  CEMFNT 

Introduction:-  The  cementing  materials  used  in  engineering 
construction  are  classified  in  Article  326-  Portland  cement  is  not 
only  the  most  important  of  these  materials  but  it  ranks  as  one  of 
the  principal  structural  materials. 

Fortlr.nd  cement  is  a  grey  powder  (some  white  Portland  cement 
is  made)  which  when  mixed  with  water  to  form  a  paste  has  the  property 
of  hardening  into  a  stone-like  mass  whether  in  air  or  under  water. 
Its  property  of  hardening  under  water  together  with  the  fact  that 
it  develops  considerable  compressive  strength  gives  Portland  cement 
a  -vide  variety  of  uses  it  would  not  otherwise  have.   It  is  rarely 
used  neat,  that  is,  as  a  mixture  of  cement  and  water.   Neat  cement 
is  too  expensive  and  besides  it  is  subject  to  excessive  shrinkage. 
Cement  is  usually  mixed  with  an  inert  material.   If  this  inert 
material  is  sand,  the  resulting  mixture  is  called  mortar;   if  larger 
broken  stone  or  gravel  is  used  with  the  sand,  the  mixture  is  known 
as  concrete.   In  both  cases  the  cement  paste  is  the  binding  material. 
Mortar  is  used  in  the  fabrication  of  stone,  brick  and  terra  cotta 
masonry;  where  used  for  surfacing  interior  and  exterior  walls, 
it  is  called  plaster  or  stucco.  AS  concrete  it  is  poured  into  molds 
to  form  monolithic  structures  such  as  foundations,  walls,  dams  and 
all  types  of  pavements.   When  steel  is  placed  in  concrete  to  take 


Civil  Engr-8.  Assignment  9.  page  2. 

tensile   stresses  tne  product   is  known  as  reinforced  concrete. 
Proper   reinforcement  makes   it  possible  to  use   concrete   for  practical' 
ly   every  type   of  engineering,   structure,    such  as  complete    ouildirigs, 
from  the   foundation  tnrough  the  columns,,  beams,   floor   slabs,  and 
walls,   to  the   roof;   and  as  "bridges,    reservoirs,   arches,   chimneys, 
and   evsn  ocean-going  ships.     Read  .article  326   in  the  text. 
Definition:-  '.Yhile  port  land  cement    is   only  an  artificial  mixture 

c^ 

of  calcareous  (which  means  lime  bearing),  and  argillaceous  (which 
means  clayey)  materials,  ourned  to  a  clinker  at  a  temperature  of 
incipient  fusion  and  afterward  ground  to  a  fine  powder.   It  is  well 
to  know  the  definition  given  in  Article  327  because  many  times  a 
verbatim  repetition  is  required. 

Incipient  fusion  is  the  stage  at  v;nich  fusion  is  just  about 
to  occur.   It  is  sometimes  spoken  of  as  initial  fusion. 
Characteristics  of  portland  cement;-    Study  Article  323.  The 
weight  of  portland  cement  is  usually  taKen  as  9<t  lb.  per  cu.  ft. 
A  sack  contains  a  cubic  foot  and  there  are  four  sacks  in  a  barrel. 
The  chemical  elements:-   Study  .urticle  329.  Remember  only  average 
figures;   lime  §2%,  silica  22%t  alumina  7%t  with  the  remainder  con- 
sisting of  iron  oxide,  magnesia,  sulphur  trioxide,  and  water, 
proportioning  of  raw  materials :-   Read  Article  330.   The  proportion- 
ing of  the  raw  materials  in  making  portland  cement  is  not  a  simple 
matter.  As  stated  in  Article  336  the  temperature  to  which  the  raw 
materials  &re  raised  is  only  sufficient  to  start  fusion  and  con- 
sequently complete  solutions  of  all  the  elements  are  not  obtained. 


Civil  Engr-3.  Assignment  9.  Page  3. 

After  calcination  the  product  is  not  a  mixture  of  clayey  and  cal- 
careous materials,  but  is  what  is  often  spoken  of  as  a  solid  solu- 
tion of  the  various  components  consisting  principally  of  silicates 
and  aluminates  of  lime.  While  the  conclusions  of  Nev/berry  and 
Le  Chatelier  have  been  shown  to  be  not  entirely  correct,  the 
methods  of  proportioning  based  on  their  conclusions  have  produced 
excellent  cement. 

Effect  of  minor  constituents:-  Read  Articles  331  to  335  inclusive. 
White  portland  cements  contain  very  little  iron  oxide.  The  color 
of  the  ordinary  port  lands  is  due  principally  to  this  oxide  of 
iron.   The  amounts  of  carbonic  oxide  are  indicated  by  the  loss  on 
ignition.   The  specified  limits  for  the  loss  on  ignition  of  sul- 
phur anhydride  and  magnesium  oxide  are  given  on  page  372  in  the 
text. 

The  consitution  of  portland  cement :-   Read  Article  336.   Portland 
cement  consists  of  a  mechanical  mixture  of  chemical  compounds  which 
have  constant  physical  and  chemical  properties.  These  compounds 
are  tricalcium  silicate  (  3  CaOSiC^),  tricalcium  aluininate 
(SCaO'AlgGs),   tricalcium  ferrite  (3CaO.Fe203)  and  calcium  ortho- 
silicate  in  the  beta  form  (2  CaO.SiOg)  given  in  the  decreasing 
order  of  their  cementing  qualities.   In  addition  to  these  compounds 
there  is  usually  about  Z%  of  gypsum.  Magnesia  in  the  form  of  the 
oxide  (JigO)  is  in  a  state  of  solid  solution  in  the  other  components, 
usually  in  such  snail  quantities  that  it  does  not  have  much  effect. 
Traces  of  other  elements  -  potassium  and  sodium  and  particles  of 


Civil  Engr-8.  Assignment  9.  page   4. 

quartz   from  the   flint  pebjle<s    in  the   ball  mills,   metallic    iron 
from  the  machinery  and  even  particles   of  semi-fused  ash,  when  coal 
is  used  as  the   fuel   in  calcining  the  cement,--  are   sometimes  found 
in  normal  port  land  cements. 

The     compounds  of  alumina,    lime,   and   silica  have  been  shown 
to  constitute  the  bulk  of  normal  port land  cement   in  studies  of  the 
ternary  ane   binary   systems  of  the  three  principal  components  by 
technicians   f ohoainta,   physical-chemists,   and  chemists)   of  various 
university  laboratories,   the  Bureau  of  Standards,   and  the  Geo- 
physical Laboratory.     A  chemical  analysis  of  a  cement  does  not 
give  the  actual  composition  because  the   results  are   in  terms   of 
the   oxides   and  the  principal  elements  do  not  exist   in  the   form  of 
oxides.      It   is  possible,   however,  to  recast  an  analysis  according 
to  known  laws   of  chemical  combination  and   obtain  the  percentage 
composition  of  the  cement   in  terms  of  the  actual  compounds  that 
exist    instead    of  the    oxides. 

Setting  and   hardening  of  portland  cement;-     Study  Article  337.     The 
setting  and  hardening   of  cement  pastes  are  defined   in  the  first 
paragraph  of  this  article.      Vvhen  mixed  with  water  the  components 
previously  mentioned   are   hydrated,  with  the  production  of  amorphous 
hydrated   silicates  and  a?_uminates   of  lime,   and   considerable  cal- 
cium hydrate    in  both  crystalline   and   amorphous  forms.      The   different 
components  do  not  hydrate  with  equal  ease.      It   is  quite   generally 
agreed  that  the  tricalcium  aluminate    is  the  first  to  hydrate   and 
that  this  compound   affects  the    initial   set.      The   tricalcium  sili- 
cate, which  has  been  found   to  have  the    greatest   cementing  value 


Civil  Engr-8.  Assignment   S.  Page   5. 

and   to  be   the   best     hydraulic   component  by  actual  experiment  ,    is 
next  to  hydrate.      It   is  this   reaction  that  causes       cement  to 
harden.     Calcium  orthosiiicate   is  the  most   inactive   of  the  cement 
components. 

Iviichaelis'   colloidal  theory  of  the  hardening,  and   setting  of 
Portland  cement   is  given  in  this  article.      Study  this  carefully 
and   be  able  to  give   it   in  your   own  words.      It   is   essentially  as 
follows:     The  hardness,    strength,   and  duraoility   of  cement  depend 
upon  the  fact  that  the  products   of  hydration  are  formed   in  the 
non-crystalline   colloidal  state.      Under  the  microscope,   freshly 
hydrated  compounds  are  non-crystalline  and  do  not  crystallize  for 
from  10  to  20  days. 

Hydration  must  begin  at  the   surfaces  -  grains   of  cement  be- 
come coated  with  colloidal  gel  -which  causes  them  to  stick  together. 
The  gel   is   impervious  and  the  centers   of  the   grains  are  not   im- 
mediately hydrated.     They  become  hydrated   only  as  water  can  diffuse 
through  the  colloid  coating.     At  this   stage  the   cement   is  not 
hard. 

The  hardening  depends  upon  the  drying  of  the  thin  coating  of 
colloid  which  envelopes  the  grains.      It   is  not  necessary  that  the 
absorbed  water   in  the  colloid  coating  evaporate   (some  does  when  the 
cement   sets   in  air).      The   free  water  may  be  taken  up  by  the  un- 
hydrated  centers   of  the  grains  and  converted   into  combined  water. 
Here    it  cannot  manifest   itself  as  -water.      (Crystals   containing  more 


than  half  their  weight   in  water,  in  the  form  *  of  crystallization, 


Civil  En-r-3.  Assignment  9.  Page  6. 

do  not  appear  tc  be  wet).   It  is  riot  difficult  to  understand  that 
cer.ent  gel  can  dry  out  in  this  manner  even  under  water.  Water  can- 
not readily  pass  from  grain  to  grain  because  of  the  impervious 
coating  of  collcid.   The  grain  centers  use  up  free  water  faster  than 
it  can  ce  supplied  from  the  outside  and  the  gel  Decodes  dry  and  hard. 
It  is  an  irreversible  colloid  and  therefore  remains  hard. 
Historical  notes;-   Read  Article  338  on  the  growth  and  importance 
of  the  Portland  csment  industry. 

Some  knowledge  of  cements,  similar  to  portland,  which  set 
under  water,  was  possesed  by  the  Romans.   It  is  said  that  the  base 
of  the  Temple  of  Castor  and  Pollux  in  the  Roman  Forum  was  a  solid 
mass  of  puzzolana  concrete. 

The  first  impetus  was  given  to  hydraulic  cements  by  John 
Smeatcn  who  rebuilt  the  lighthouse  on  Eddystone  Rock  in  1756.   See 
Article  587  on  page  365  in  the  text. 

About  fifty  years  later  the  French  chemist  Vicat  produced  a 

product  similar  to  that  used  by  Smeaton.  Vicat 's  semeni  •-;?&$  produce^ 
by  burning  a  finely  pulverized  chalk  and  clay  after  he  had  mixed 

them  to  form  a  paste. 

The  first  patent  was  granted  in  182<±  to  Aspdin,  a  Yorkshire 
bricklayer,  who  heated  pulverized  chalk  with  clayey  river  mud. 
Because  of  a  fancied  resemblance  (actually  there  was  very  little) 
between  his  product  and  a  well  known  limestone  quarried  near 

• 

Portland  (which  is  on  the  South  East  coast  of  England)  and  known 
as  Portland  stone,  he  named  it  Portland  cement.   The  name  has  been 
universally  adopted.   Aspdin  is  usually  given  credit  for  the  in- 
vention of  portland  cement. 


Civil  £ngr-8.  Assignment  9.  Page  7. 

In  1874  the  first  port  land  cement  was  made  in  the  United 
States.   In  I92U,  100,302,000  barrels  were  produced  at  an  average 
cost  of  $2.01  per  barrel. 

Ra-7  materials;-  Read  Article  339.   Some  of  the  rav;  materials 
used  by  California  plants  are  as  follows:  The  Standard  Portland 
Cement  Company  at  Napa  Junction,  Napa  County  uses  a  pure  limestone 
end  a  clayey  limestone;  the  California  Portland  Cement  Company 
at  Gait on,  San  Bernardino  County,  uses  clay  and  a  pure  limestone; 
the  C owe  11  Portland  Cement  Company  at  C owe  11,  at  the  foot  of  Mount 
Diablo  near  Concord,  Contra  Costa  County,  uses  travertine  and 
shaiy  clay;  the  plant  of  the  Santa  Cruz  Portland  Cement  Company, 
at  Davenport,  just  north  of  Santa  Cruz,  uses  shale  and  a  pure 
limestone;  the  Riverside  Portland  Cement  Company  operates  a 
plant  at  Riverside  using  a  mixture  of  clay  and  limestone. 
Manufacture  :-   Study  Articles  340  to  349  inclusive,  they  describe 
the  manufacture  of  port land  cement  by  both  wet  and  dry  methods. 
Most  cement  manufactured  in  the  United  States  is  made  by  the  so- 
called  dry  process.   Only  one  California  plant,  that  at  San  Juan 
(just  south  of  Gilroy),  making  the  Old  Mission  brand,  uses  the  wet 
method  of  manufacture.   Crude  oil  is  the  fuel  used  in  the  Cali- 
fornia cement  mills. 

The  average  temperature  of  burning  is  about  2,800°  Fahren- 
heit.  In  most  plants  the  clinker  is  cooled  in  air  but  if  it  is 
cooled  as  stated  in  Article  345,  by  being  sprayed  with  water,  note 
that  the  water  does  not  injure  it.  Clinker  has  no  cementing 
properties;   it  must  first  be  finely  ground. 


Civil  Lngr-8. 


Assignment   9. 


page   8. 


The   amount   of  gypsum  which  can  be   added   after   the   cement 
has   been  buried    is   Z%,      It    is  added   to  retard   the   set   of  the   cement. 

Be   aoie   to  -visualize   the  process   of  manuiacture   as   indicated 
in  the   following  diagram: 


ff 


V 


§ 

O. 

O 


en 
o 

•c 
s  ^ 

p   o 

r»-  0> 
0> 
"«    O 

H.    Mj 

P 

H-1  » 

tn   P 


H- 

A 


I 


SB 
M 

"=W 

PS 


co  Hr 
o  o 

P  -o 

I-"  0 
CD    *J 
to   <:*• 

H- 

0 
3 
H- 
3 
<fi 

H-    >1 

d.   (B 

H«  *T! 

3 

O 
CO    h-1 
c*-  H. 
0    3 

OJ 
3- 


en 


Civil  Engr-8.  Assignment  9,  Page  10- 

Conditions  Affecting  the  Properties  of  Cement:-   Read  Articles  350 
to  354  inclusive.   The  properties  mentioned  in  these  articles  will 
be  described  in  detail  in  Chapter  XII  begining  on  page  371  in  the 
text. 

Soundness  is  the  most  important  property  of  cement.   Un- 
sound cement  cracks  and  disintegrates  after  it  has  set.   It  is 
thought  that  the  principal  element  causing  unsoundness  is  free  lime. 
Thorough  seasoning,  fine  grinding  of  the  raw  materials  and  the 
clinker,  and  the  use  of  the  nininum  amount  of  gypsum  tend  to  pre- 
vent unsoundness. 

Fineness  of  grinding  is  the  principal  factor  affecting  the 
tensile  strength  of  cement  :nortf>r.   The  tensile  strength  of  sand 
mortars  is  improved,  "but  that  of  neat  cement  mortar  is  decreased  by 
fine  grinding. 

The  time  of  set  is  decreased  by  fine  grinding  of  the  cement. 
Finely  ground  cements  sometimes  develop  a  flash  set  which  makes 
them  unfit  for  use  in  engineering  structures.   The  degree  of  season- 
ing, the  temperature  of  the  air  and  the  mixing  water  all  affect  the 
time  of  set. 

The  fineness  of  cement  is  influenced  by  the  hardness  of  the 
klinKer  and  the  efficiency  of  the  grinding  machinery  used.   There  is 
no  relation  bet-ween  the  strength  of  concrete  and  the  fineness  of 
cement  if  different  cements  are  considered. 

Long  seasoning  is  the  chief  cause  of  a  low  specific  gravity 
of  cement. 


. 


Civil  Engr-8.  Questions  to  Assignment   9.  page   11. 

1.  Define   ^Ttland   cement. 

2.  Explain  the  derivation  of  the  term  port land  in  the  name 
Portland  cement. 

3.  Outline  the  process  of  manufacture  of  portland  cement. 

4.  What  are  the  nair.es  of  the  principal  constituents  of  portland 
cement? 

5.  State  the  colloidal  theory  of  setting  and  hardening  of  cement 
as  advanced  "by  Michaelis. 

6.  What  is  the  temperature  at  which  cement  is  calcined? 

7.  What  is  meant  by  incipient  fusion? 

8.  How  does  fine  grinding  effect  the  strength  of  neat  cement 
mortar? 

9.  What  is  the  principal  cause  of  unsoundness  in  cement? 

10.  Define  unsoundness. 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 

Assignment  10. 
Civil  Engr-e.A^.  Professor  C.T-  Wiskocil 

PORTLAND  CELERY  (continued)  and  NATURAL  CEi&NT 
Tensile  and  compressive  strength  of  cement;-  Read  Articles  355 
and  356.  As  has  already  been  mentioned,  neat  cement  is  rarely  used 
in  engineering  construction.  Recently  it  has  been  used  to  make 
joints  in  laying  be 11-and -spigot  cast  iron  pipe.   The  cement  is 
mixed  with  juwt  enough  water  to  hydrate  it  so  that  when  ready  for 
use  it  is  not  a  paste  but  is  merely  moist.   In  this  condition  it 
can  be  rammed  into  the  joint  where  it  hardens  -without  shrinkage 
cracks.   These  joints  have  been  very  successful. 

Most  of  the  tests  on  neat  cement  were  made  during  the  develop- 
ment and  standardization  of  this  important  structural  material. 
Those  reported  in  Bulletin  333  of  the  United  States  Geological 
Survey  (mentioned  in  Article  356)  were  made  in  the  period  from 
1905  to  1907.  They  were  published  in  1908.   Sinr:e  that  time  it 
has  been  found  that  the  strength  of  neat  cement  is  no  criterion  of 
the  strength  of  mortar  or  concrete  made  from  it.  Furthermore, 
tensile  strength  tests  of  a  given  cement  h?.ve  been  found  to  be  de- 
cidedly influenced  by  the  methods  of  mixing  and  molding  and  other 
variables  that  may  be  grouped  into  what  is  called  the  personal 
equation.   Standard  specifications  once  included  the  test  of  neat 
cement,  but  it  should  be  noted  that  at  the  present  time  only  a 
1  to  3  standard  sand  mortar  is  tested  (see  page  372  of  the  text). 


.    • 

;.-;         . 


Civil  Engr-S.  Assignment  H>.  page   2. 

The  data  given  in  Figure   13  on  page  331  do  not  checic  tnose 
given   in  Figure   16  on  pa^e  335.     Remember  that   in  addition  to  the 
personal  equation,   conditions   of  storage t  temperature   of  mixing 
water,   form  of  briquette,   and  amount  of  mixing  water  used  all  effect 
the   strength  of  the  cement:     moreover,   different  brands  have   in- 
dividual qualities.      The  principal  difference  between  the  sets   of 
data  mentioned   is  that  those    in  Figure   16  do  not  show  the  decided 
decrease   in  strength  at  the  age   of  one  year.      Since  the  tensile 
strength  of  neat  cement   is  not   inportant   it   is  sufficient  to  remem- 
ber that  the   strength  increases  with  age  to  a  maximum  of  about 
1,000  Ib.   per   sq.    in* 

The  cornpressive   strength  of  neat  cement  also  varies  with 
age,  the   size  and   shape   of  the  test-specimen,   and  the  amount  of  mix- 
ing water  used.      The  consistency  of  the  freshly  made  cement  paste 
varies  considerably  with  the  amount   of  water  used;  yet,    in  spite   of 
the  fact  that  this  factor  has  a  great   influence   on  the  ultimate 
strength  of  the  hardened  mortar,    it  v/as   seldom  recorded   in  early 
experiments,    such  as  these  used   in  preparing  Figure   14  in  the  text. 
The  data   in  Figure   14   shew  that  the  c oppressive    strength  of  neat 
cement   one  year   old  varies  from  about   11,OCO  to   13,000  Ib.    per   sq. 
in.      Some  tests  reported  by  A.C.   Alvarez   in  THE  C OPPRESSIVE  STRENGTHS 
OF  PORTLAND  CEfcENT  hCHTARS   OF  VARIOUS  PROPORTIONS,   University  of 
California  puoiications  in.  Engineering  (1915),   give  the  compressive 
strength  of  neat  cement  mortar  cubes,   4&  days   old,  as  10,000  Ib. 
per.    sq.    in.      The  cement  paste  was  of  normal  consistency,   ZZ%  water 


Civil  -Engr-8.  Assignment  10-  Page   3. 

being  used.      Increasing  the  amount   of  mixing  water  v;ould  decrease 
the  ultimate  strength.      The   relation  would  prooably  be   similar 
to  that  shown  in  Figure   1   on  page   816   in  the  text.      The  effect   of 
the  variaale  amount   of  mixing  water  and  another  variaole,   the  mold- 
ing pressure,    is  clearly  shown  in  an  article,  PRESSING  OUT  MIXING 
WATER  ADDS  TO  CEAiErIT  IIORTAR  STRENGTH  bj,   C.I.   Wiskocil,  Engineer ing - 
News  Record,   83,    13C   (July   17,    1919).      The  following  facts  are 
taken  from  that  article:      "Neat  cement  mortar  made  with  25%  water 
had  a  compressive   strength  of  6,800  ID.    per   sq.    in.    at  7  days.      In- 
creasing the  amount   of  water  to  37$  reduced  the  7-day  strength  to 

2,500  Ib.    per   sq.    in.      The  paste  used   in  making  the   latter   speci- 

WAS 
mens ^we**  molded  under  a  pressure   of  about  30,000  Ib.    per   sq.    in., 

TKe4€    f  resort 

allowing  the  expressed  water  to  escape,   Dr oduo ec   spec imens  whoae 
d  # 

7-day   strength  w«a^l7,000  Ib.   per   sq.    in." 

Since  the   strength  of  neat  cement   is  not.   important,   take 
10,000  Ib.    per   sq.    in.   as  the  average  eonipressive   strength.      It   is 
easily  remembered  with  the   1,000  lo.    per   sq.    in.    for  the  average 
t.SRsile   strength. 

"Expansion  and   contraction  dae   to  changes   in  moisture   content :- 
Read  Article   357.      The    important   fact    is  that   dry  mortar   as  well  as 
concrete    (see  Article   522   on  page   480   in  the  textj  will  expand 
when   it  becomes  vTet   and   contract  again  upon  drying.      Frequent ly 
changes   in  moisture  content  are  as   important  as  temperature 
changes   in  producing  variations   in   linear   and   volumetric   dimensions 
of  mortar   and   concrete. 


Civil  Engr-8.  Assignment  10.  Page  4. 

Effect  of  remixing  on  the  strength  of  cement ;-   Read  Article  358. 
The  practice  of  using  cement  that  has  set  is  seldom  allowed  in 
engineering  construction.   Remixing  is  the  use  of  set  cement  while 
retempering,  is  the  addition  of  water  to  set  cement;  but  since 
neither  practice  is  in  general  use  the  subject  is  not  important. 
Remixed  mortar  is  frequently  used  in  laying  floor  and  v/all  tile 
because  of  the  impression  among  the  artisans  that  this  procedure 
increases  the  cementing  qualities  of  the  mortar.  The  data  in 
Figure  21  show  that  the  compressive  strength  of  neat  cement  mortar 
is  not  materially  affected  by  remixing  even  several  hours  after  it 
has  been  prepared. 

The  central  mixing  plant,  which  necessitates  some  long 
hauls  of  wet  concrete,  is  frequently  used  in  road  construction, 
particularly  on  large  contracts.  Recent  tests  by  the  Bureau  of 
Public  Roads  show  that  the  compresaive  strength  of  concrete  will 
not ''be  affected  so  long  as  it  remains  workable.  Test  specimens 
mace  from  wet  concrete  which  had  been  hauled  in  trucks  for  periods 
up  to  three  hours  showed  no  appreciable  decrease  in  compressive 
strength.  The  concrete,  howerer,  became  too  dry  for  hand  finishing 
45  minutes  after  it  had  been  prepared.  These  remarks  are  inserted 
at  this  point  uecause  the  subject  is  not  discussed  under  CONCRETE 
in  the  text. 

Effects  of  high  and  low  temperature  on  ceiaent;-    Read  Articles 
359  and  360.  The  setting  and  hardening  of  cement  paste  is  retard- 
ed and  may  oe  entirely  stopped  by  decrease  in  temperature.  These 
effects  are  not  appreciaole  until  the  temperature  falls  below 


Civil  Engr-8.  Assignment  1C. 

40  degrees  Fahrenheit,   Alternate  freezing  and  thawing  of  cement 
before  it  sets  is  particularly  harmful. 

High  temperatures  produce  marked  reductions  in  the  strength 
of  cement  mortar.  Remember  that  cement  begins  to  fuse  at  approxi- 
mately 2,800  degrees  Fahrenheit. 

Temperature  of  cement  during,  period  of  set;<-     The  effect  of 
alkali  on  the  durability  of  cement  concrete  is  being  intensively 
studied  at  the  present  time.  As  yet  no  conclusions  are  available. 
There  are  numerous  examples  of  failure  of  cement  subjected  to  the 
influence  of  alkali  but  the  history  of  the  preparation  of  the  con- 
crete, v;hich  is  thought  to  have  considerable  effect  on  its  dura- 
bility, is  not  always  available. 

Sugar  and  animal  and  vegetable  oils  disintegrate  cement  mortar 
and  concrete. 

Effect  of  storage  on  cement :-    This  subject  is  not  satisfactorily 
discussed  in  the  text  (see  page  373)  but  it  is  one  that  can  -.be 
taken  up  at  this  point.  The  question  is  important  because  a 
shortage  of  fresh  cement  on  a  joo  will  frequently  necessitate  the 
use  of  cement  that  has  been  stored  from  six  months  to  a  year  or 
produce  an  enforced  delay  until  a  new  shipment  can  be  secured. 
The  storage  of  cement  is  of  interest  to  the  manufacturer  and  dealer 
as  well  as  the  user  oecause  it  is  becoming  the  practice  tc  deliver 
concrete  materials  on  the  job  prior  to  the  opening  of  the  construc- 
tion season.   The  principal  study  of  this  question  has  been  made 
at  the  Structural  Materials  Research  Laboratory,  Lewis  Institute, 


Civil  Engr-3.  Assignment  10.  page  6. 

Chicago,  and  reported  in  Bulletin  6,  EFrECX  OF  STORAGE  OF  CE&ENT,  by 
D-A.  Abrams. 

The  cement  was  stored  in  cloth  and  paper  sacks  under  three 
different  conditions;  namely,  indoors  v;ith  uniform  temperature  and 
low  humidity,  indoors  at  lower  temperature  and  higher  humidity 
(average  basement  conditions),  and  under  average  shed  conditions, 
which  afford  protection  from  direct  contact  with  rain  and  snow  but 
allow  free  circulation  of  outside  air  with  variable  temperature 
and  humidity. 

The  principal  conclusions  are  the  following:  There  is  no 
marked  difference  in  the  quality  of  the  cement  stored  in  paper  and 
cloth  sacks  for  periods  up  to  1  1/2  years  of  storage.  The  exact 
condition  of  storage  is  not  of  ^reat  importance  so  long  as  the 
cement  is  protected  from  direct  contact  with  moisture. 

• 

The  deterioration  of  stored  cement  is  probably  due  to  the 
absorption  of  moisture  fron  the  air,  which  causes  a  partial  hydra- 
tion  of  the  cement.   The  principal  effect  on  the  mortar  and  concrete 
making  qualities  are  the  decrease  of  early  strength  and  the  pro- 
longing of  the  time  of  setting. 

The  effect  of  storage  is  clearly  shown  in  the  accompanying 
diagram. 


Civil  Engr-8. 


Page  7 


0     4      8     12     16     20     24 

Age  of  test  specimens,  in  months 

The  Effect  of  Storage  of  Cement  on  the  compressive  strength  of  1-5 
concrete  tested  at  different  ages. 

The  compressive  strength  of  concrete  and  mortar  showed  a 
decrease  in  strength  with  storage  of  cement  for  all  samples,   for 
all  conditions  and  periods  of  storage  and  at  all  test  ages.   The 
decrease  was  greatest  for  the  samples  stored  in  the  shed  and  nearly 
as  great  under  basement  storage. 

The  age  of  the  concrete  has  a  large  influence  on  the  re- 
sults obtained.   Taking  the  poorest  condition  of  storage,  that 
under  the  shed,  the  specimens  tested  at  the  age  of  7  days,  made 
from  cements  and  all  periods  of  storage,  was  64$  of  the  strength 
of  the  specimens  made  with  cement  when  received  from  the  vrarehouse; 
at  28  days,  71%;  at  6  months,  73%:  at  1  year,  S2%  and  at  2  years 
85%.   Similar  results  were  obtained  from  specimens  under 


Civil  Engr-8.  Assignment  10.  page  8. 

other  conditions  of  storage.   These  data  tend  to  show  that  the 
strength  of  concrete,  say  3  or  4  years  after  it  has  been  poured, 
is  not  affected  "by  the  length  of  time  (age)  the  cement  was  stored 
prior  to  use. 

The  use  of  reclaimed  cement,  that  is  cement  that  is  obtained 

cement 
from  used/sacks  of  pneumatic  methods  or  shaking,  is  questionable 

practice  and  should  not  be  permitted  on  any  engineering  structure. 
Effect  of  fineness  of  cement;-   Fineness  is  a  distinct  property 
of  cement  and  should  be  discussed  at  this  time.   It  is  briefly 
noted  on  page  322  in  the  text.  The  most  important  tests  were  made 
by  D.A.  Abrams  and  reported  by  him  in  EFFECT  OF  FINENESS  OF  CEMENT 
in  the  Proceedings  of  the  American  Society  for  Testing  katerials, 
Vol  XIX,  part  II,  1919.  The  following  are  his  principal  con- 
clusions : 

There  is  no  necessary  relation  between  the  strength  of 
concrete  and  the  fineness  of  the  cement,  if  different  cements  are 
considered. 

In  general,  the  strength  of  concrete  increases  with  the 
fineness  of  a  given  lot  of  cement. 

Fine  grinding  oi  cement  is  more  effective  in  increasing  the 
strength  of  lean  mixtures  than  rich  ones. 

The  principal  result  of  finer  grinding  of  cement  is  to 
hasten  the  earl;/  hardening  (strength;  of  the  concrete. 

Fine  grinding  of  cement  reduces  its  time  of  set. 

Ordinary  concrete  mixtures  shov  an  increase  in  strength  of 
about  l.&%  for  \%  reduction  in  the  residue  of  the  cement  on  the  No. 


Civil  Engr-8.  Assignment   10.  page   9. 

2CO  sieve.      (Kemember  that  the  fineness   is  measured   by  the   residue 
on  a  No.    2uO  sieve . ) 

It  has  been  found   by   other   investigators  that  the  principal 
cause   for   rejection  of  finel^   ground  cement   is  the  development   of 
a  flash  set  after  delivery;   the  mill  tests   shoeing  the   cement  to 
be  normal  at  the  tiire    cf  shipment. 

Natural  cement:-       Keac  Articles  365  to  369   inclusive   on  natural 
cement.     When  clay-bearing   limestone   is  heated   to  about  200C  de- 
grees Fahrenheit,    it   g.ivea   off  carbon  dioxide   and  forms  a  clinker, 
•which  when  finely   ground    is  knov;n  as   natural  cement.      The   clinker 
will  not  ^.ir   slr.ke  but  when  mixec  vith  water   the   resulting  paste 
•will  harden  in  air   or  under  vjater   just  as  portland  cement  does. 

Natural  cement   is  not  as  uniform  as  portland  cement  ar\d   it  has  less 

15 
strength.      In  spite   cf  its  cheapness   H    *«  very  littleAused.      It 

has  been  used   for  mortar  for  masonr^    and  ior  concrete  where 
strength  we. 6  not  a  r,rir:e   requisite. 

Miscellaneous  cements:-       Read  Articles  370  to  373   inclusive.     White 
portland   cement   is   crobajiy  the     jiost   important   of  the  varieties 
mentioned.      It    is   impossible  to  get  the   proper   shades   cf  color   in 
stucco  made  with  colored   aggregate  when  using  the    ordinary   grey 
portland   cement;     white   portland   cement    is  used   almost  exclusively 
for   this  purpose.      In  the  construction  of  light  colored  masonry 
it   is   necessary  to  have   a  mortar   that  will  not   stain  the   stone. 
\Vhite   portland    is  much  more    satisfactory  than  a  natural   cement 
(which   is  also   stainless)   for   this  purpose. 


Civil  Engr.-8.  Assignment  10.  Page  10. 

Pazzolana  cement:-   iazzolana  is  the  name  used  in  Europe  to  desig- 
nate the  cements  made  from  volcanic  material.   These  were  first 
used  as  a  cementing  meter ial  at  pczzuoli,  Italy,  Puzzolan  (pro- 
nounced pot-S'.vo-lan)   cements  v;ere  widely  used  in  the  days  of 
the  Roman  Empire.  A  fe-.v  of  the  structures  made  at  that  time  are 
still  in  a  fair  state  of  preservation.  This  class  of  cements  in- 
clude all  hydraulic  cementing  materials  ^/hich  are  made  by  the 
incorporation  of  natural  or  artificial  puzzolans  v;ith  hydrated 
lime  without  subsequent  calcination.  The  only  natural  puzzolan 
materials  of  importance  are  puzzuolana,  trass,  and  tuff  or  tufa. 
Blast  furnace  sla^,  ie  an  artificial  puzzolan  materiel.  PC  not  con- 
fuse the  so-called  slag  ceuent  with  the  true  portland  cement  made 
•with  blast  furnace  slag.   The  tufa  cement  used  in  the  construction 
of  the  Los  Angeles  aqueduct  was  neither  a  true  pert land  nor  c  true 
puzzolan  cement.   It  was  a  blended  ce:ient  as  described  in  Article 
572. 

These  blended,  improved,  or  puzzol&n  cements  are  never 
brought  into  competition  ^ith  portland  cement  where  ^reat  strength 
is  required. 

Alumina  cements^:-    Alumina  cements  are  not  discussed  in  the  text 
probably  because  they  have  nexer  been  made  on  a  commercial  scale 
in  this  country.   In  France,  where  they  were  produced  first,  they 
are  only  now  coming  into  .general  use. 

Alumina  cements  differ  from  portlend  cements  in  che.racil 
composition  and  the  rate  of  hardening.  Both  mortars  and  concretes 


Civil  Engr-3.  Assiemmeut  10.  Page  11. 

develop  greater  strength  within  48  hours  (and  in  most  instances 
within  24  hours)  than  corresponding  mixtures  made  with  portland 
cement  develop  in  28  days.  Furthermore,  alumina  cements  have 
great  resistance  to  the  action  of  sea  water  and  alkali -"bear  ing 
•waters. 

Investigations  on  these  cements  were  begun  about  1902  by 
H.S.  Spackman  and  E.  W.  Laze  11  in  the  United  States.   In  France, 
J.  Bied  began  his  studies  on  this  material  in  1908*  Recently 
P.  H-  Bates  of  the  United  States  Bureau  of  Standards  has  reported 
on  his  study  of  alumina  cements.   In  1912  the  firm  of  J.  and  A. 
Pavin  Lafarge  marketed  alumina  cement  under  the  name  of  CE&ENT 
FONDU.   It  was  manufactured  for  military  use,  only  during  the  war, 
but  in  1919  its  commercial  use  was  resumed. 

The  approximate  composition  of  alumina  cement  is  50$  lime, 
4C$  alumina  and  IQf*  silica  and  impurities.   It  is  sometimes  referred 
to  as  a  mono-calcic  aluminate.   It  is  low  in  lime  and  silica,  and 
high  in  alumina  as  compared  with  normal  portland  cement.   In 
France  it  is  made  in  small  blast  furnaces  which  are  charged  with 
coke,  limestone  and  bauxite.  The  fused  slag  or  clinker  is  cooled 
and  ground.   If  the  bauxite  is  pure  the  cement  is  white  in  color 
but  the  commercial  cements  are  dancer  than  Portlands  because  of  the 
impurities  in  the  raw  materials.   Since  actual  fusion  is  not 
necessary  this  cement  could  be  made  with  the  same  machinery  used 
in  the  manufacture  of  portland  cement.  The  cost  of  manufacture  of 
the  cements  would  be  about  the  same  but  the  actual  cost  of  alumina 
cement  is  dependent  upon  the  cost  of  bauxite  which  at  present  would 


Civil  Engr-8.  Assignment   10.  page    12. 

bring  it   over  that   of  ordinary  port land   cement. 

Alumina  cements  are   slow  setting  and  are  gaged   like  the 
ordinary  port land  cement,     heports  on  the  French  cements  give,   for 
a  1:1:3  gravel  concrete,  compressive   strengths   of 

7,500  Ib.  per  sq.  in.  at  3  days 
8,500  lo.  per  sq.  in.  at  28  days 
9,000  Ib.  per  sq.  in.  at  3  months 

Other  reports   sta^e   that  a   1  to  3   sand  mortar  developed   75%  of   its 
own  28-day   strength  in  24  hours.     During  the  war  heavy  guns  were 
moved   on  alumina-cement -concrete   foundations   24  hours  after  they 
had  been  poured. 


Civil  Engr-8.      Questions  to  Assignment  10.          page  13. 


1.  How  does  a  change  in  moisture  content  of  hardened  cement  mortar 
effect  its  volume? 

2.  Give  the  approximate  tensile  and  compressive  strengths  of 
neat  cement  mortar. 

3.  Name  the  various  factors  that  affect  the  strength  of  cement 
mortars. 

4.  Does  the  long  haul  of  wet  concrete,  made  necessary  by  the  use 
of  central  mixing  plants,  affect  the  strength  of  the  hardened 
concrete? 

5.  What  is  the  principal  precaution  to  be  taken  when  storing 
cement  ? 

6.  Would  you  allo?/  the  use  of  cement  that  had  been  stored  on  the 
job  -  say  for  18  months? 

7.  Under  what  conditions  would  you  allow  the  use  of  so-called 
reclaimed  cement? 

8.  How  does  the  fineness  of  the  cement  affect  the  time  of  set  and 
what  is  the  importance  of  time  of  set? 

9.  What  is  the  relation  between  the  strength  of  concrete  and  the 
fineness  of  the  cement  used? 

10.  Differentiate  between  slag  cement  and  portland  cement  made  from 
blast  furnace  slag. 

11.  Will  natural  cement  set  under  water? 


UNIVERSITY  OF  CAL  IF  CRN  IA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials   of  Engineering  Construction 

Assignment   11. 

Civil  Engr-8. A.  Professor  C-T.  Wiskocil 

LIMB 

Introduction:-   Line,  as  used  in  the  preparation  of  mortar,  was 
one  of  the  building  materials  used  by  the  early  Greeks  and  Romans. 
Probably  the  earliest  known  use  of  line-mortar  was  in  the  con- 
struction of  the  Egyptian  pyramids.  During  the  recent  war  the  manu- 
facture of  lime  was  declared  to  be  an  essential  industry,  not  be- 
oause  of  its  use  in  building  construction  -  although  large  quanti- 
ties were  used  in  the  construction  of  buildings  by  the  United  States 
Housing  Corporation  -  but  on  account  of  its  importance  as  a  chemical 
reagent  in  the  manufacture  of  guncotton,  leather  and  other  essential 
products . 

Definition  and  classification:-   Lime  is  the  product  obtained  by 
heating  limestone  so  as  to  drive  off  the  carbon  dioxide.   It  is, 
therefore,  a  calcium  oxide.   Study  Article  379;   it  contains  a  more 
detailed  definition  and  a  partial  classification  of  lime.  There 
are  two  general  grades  of  lime;  selected  and  run-of-kiln,  both  of 
which  are  described  in  the  article  noted.  Lime  is  frequently  sold 
as  lump  lime,   in  -which  the  size  of  the  individual  pieces  is  left 
as  they  come. from  the  \kiln, '.and  pov.'dered  lime,  which  is  oroken  up 
so  that  it  will  all  pass  a  1/4  inch  screen.  The  classification 
adopted  by  the  American  Society  for  Testing  Materials  is  referred 


Civil  Engr-3-  Assignment   11.  Page  2. 

to  in  Article   379;    it   is  as  follows:       high  calcium  lime,   not  less 
than  90^  calciur  oxide;  calcium  lime,   not   less  than  85  or  more 
than  9C/o  calcium  oxide;     magnesian  lime,   not   less  than  10  nor  more 
than  25$,  magnesium  oxide;  and  high  magnesian  lime,   not   less  than 
25$     magnesium  oxide.      If  these   limes  contain  less  than  5f0  of 
silica,   alumina,  and   iron  oxide,  which  are  known  as   impurities, 
they  are  called   rich  or   fat   limes.      Limes  containing  more  than  5$ 
of  these   impurities    (noted  adovej   are  known  as  poor   or   lean  limes. 
Sometimes   lime   is  classified  according  to  the   purpose  for  which   it 
is  best  fitted,  as  agricultural,  building,   finishing,   or  chemical 
lime. 
Manufacture  ;~       Study  Article  380  and   read  Article  381.     While   lime- 


-  - 
stone  has  been  described  before,   rege&p  some   of  the   important  facts 


about   it  ::.since    it   is  the  raw  material  from  which   lime   is  made. 
Since    limestone   is   of  sedimentary   origin  it   is  never  found   pure.      It 
is  essentially  calcium  carbonate  with  impurities   of  magnesia,    iron, 
alumina,   and   silica.     Very  pure  cyrstallized   limestone   ie  called 
calcite.      when  the  amount  of  magnesia  increases   it   is  called 
magnesian   limestone  until  the   ratio  of  calcium  to  magnesium  caroon- 
ate   becomes   100  to  84;      it   is  then  called  dolomite.      When  magnesia 
remains   low  but   impurities   increase,   the  rock  may    tie  an  argillaceous 
limestone,   natural  cement   rocic,    or  calcareous   shale. 

There  are  three  principal  types   of  kilns  for  burning  lime; 
the   pot  kiln,    the   patent  kiln  and   the   rotary  kiln.      The  mixed-feed 
type   described    in  the  text   is  the  pot  kiln.      The   separate-feed  type 


Civil  Eiigr-8.  Assignment  11.  Page  3- 

is  the  patent  kiln,  and  is  the  best  type. 

As  indicated  in  Article  37S  the  reaction  produced  in  the 
heating  cf  limestone  is  essentially 

CaCG,  -r  heat  — «*  QaO  -t-  CO,, 
w  2 

The  carbon  dioxide  is  driven  off  as  a  gas  which  leaves  the  lime  as 
a  mixture  of  oxides.   The  amount  of  heat  required  depends  upon  the 
chemical  composition  of  the  stone.   Under  ordinary  conditions  cal- 
cium carbonate  breaks  ur  at  898 °C  (1648°  F- )  When  the  temperature 
reaches  about  219G°F,  the  calcium  oxide  and  the  impurities  in  the 
stone  combine  to  form  compounds  that  produce  partial  vitrification 
and  retard  the  slaking  of  the  lime.  The  required  amount  of  heat 
may  be  supplied  quickly  at  a  high  temperature  or  over  a  longer 
period  at  a  lower  temperature.   Since  the  activity  of  the  impuri- 
ties becomes  noticeaule  belovv  21GO°F-  ,  better  quality  is  secured 
at  lower  temperatures  of  ourning.  Wood-burned  lime,  oecause  of 
the  lower  temperature  of  burning,  usually  commands  a  higher  price 
than  coal-burned  lime.   The  introduction  of  steam  into  the  kiln 
during  the  burning  process  tends  to  increase  the  quality  of  the 
lime  by  decreasing  the  temperature  of  decomposition  from  1648°F 
to  aoout  1450°F. 

Slaking  or  hydration  of  lime;-   Study  Article  382.   Quicklime  is 
prepared  for  use  in  building  construction  by  slaking  *hich  is  the 
addition  of  water  to  form  a  paste.   Slaking  is  a  process  of  hydra- 
tion, in  which  the  calcium  oxide  combines  with  -water  to  form  the 
hydroxide. 


• 


Civil  Fugr-8.  Assignment  11. 

CaO  T  h20  — 9-  Ca  (QHJg 

Slaking  is  usually  done  in  a  shallow  watertight  box.   The  water  is 
poured  over  the  lime.   Hiah  calcium  lime  must  de  stirred  continu- 
ously to  prevent  the  heat  generated  from  ourning  the  lime.   The 
•water  absorbs  the  excess  heat.   Too  much  water  lowers  the  tempera- 
ture and  retards  the  slaking,  impairing  the  plasticity  of  the 
product.  The  addition  of  too  much  v;ater  is  known  as  drowning.  A 
high-caiciuir.  lime  is  subject  to  burning,  while  the  slaking  of  a 
high-magnesian  lime  must  be  watched  to  prevent  drowning.  A  skilled 
operator  is  required  to  slake  quicklime  properly.  Both  underburned 
and  over burned  lime  will  slake  more  slowly  than  that  which  is  prop- 
erly burned.  The  rate  of  hydration  (slakingj  indicates  the  burning 
temperature.   Slaked  lime,  which  is  a  thick  paste,  is  sometimes 
called  lime-putty.   It  will  keep  indefinitely  if  it  prevented  from 
drying  out.   It  is  stored  in  casKs  or  in  the  boxes  in  which  it  is 
made.   It  w5.11  not  harden  under  water. 

Setting  and  hardening:-    The  setting  is  caused  by  the  evapora- 
tion of  excess  water  from  the  lime  paste.   Hardening  is  a  chemical 
action  involving  the  replacement  of  the  water  in  the  hydroxide  by 
car  con  dioxide,  with  the  result  that  the  lime  paste  reverts  to  the 
calcium  carbonate.   Hardening  is  accelerated  by  increasing  the 
amount  of  carbon  dioxide  in  the  air  and  by  the  use  of  moist  air. 
The  first  condition  is  produced  by  the  use  of  salamanders  and  the 
second  by  the  frequent  wetting  of  mortar.   These  methods  are  used 
in  hardening  interior  plastering 


Civil  Engr-8.  Assignment  11.  Page  5. 

Properties  of  lime:-   Study  Article  385.   In  general,  lime  is  a 
white  substance  which  v.rill  slake  when  water  is'  added  to  it.  Dur- 
ing the  slaking  process  the  "w^ter  enters  into  chemical  combination 
r?ith  the  lime  with  a  resulting,  generation  of  heat  and  increase  in 
•volume.  When  exposed  to  air,  slaked  lime  will  set  and  harden. 
The  carbon  dioxide  from  the  air  combines  with  the  lime  and  forms 
the  carbonate.   Setting  is  always  accompanied  by  a  decrease  in 
volume. 

Lime  when  exposed  to  air  will  air-slake  as  described  in 
Article  382.   This  term  air-slaked  lime   is  rather  confusing,  be- 
cause the  substance  is  practically  identical  with  finely  ground 
limestone  and  therefore  has  no  value  as  lime  for  structural  pur- 
poses. 

The  strength  of  lime  mortar  depends  principally  upon  the 
method  by  which  it  is  prepared  and  the  kind  of  sand  used.  Mortar 
made  with  dolomitic  lime  is  generally  stronger  than  that  made  with 
high-calcium  lime.  This  may  be  due  to  the  fact  that  the  greater 
shrinkage  in  high-calcium  lime  mortars  may  tend  to  weaken  the  oond... 
Moreover,  magnesian  mortars  are  made  up  with  less  water  so  that 
they  contain  more  actual  binding  material;  and  again,  since  high- 
calcium  limes  will  carry  more  sand  they  are  frequently  overloaded; 
that  is,  the  proportion  of  lime  paste  to  sand  is  relatively  large 
and  hence  the  resulting  mortar  is  weak. 

Lime  mortar  is  never  used  where  strength  is  required.   The 
choice  between  limes  should  be  made  not  on  the  basis  of  strength 
but  rather  on  relative  cost  and  previous  experience. 


Civ;.I  Fingr-8. 

Lor  tar   joints   ir.  iTK-,soury  are   seldom  over    1/2   inch  thick.      The 
actual  resistance   to  c oppressive    loads   is  therefore   greater  than 
indicated   in  the  tables     such  as  the   one  given  on  page   364. 
Commercial  forms:-     Lime   is  put   on  the  market   in  two  forms,    lump 
and   ground.      Lump   lime    is   shipped    in   DulK  and    in  wooden  barrels   of 
180   or   280   Ib.    net  capacity.      Ground    lime    is   screened   through  a 
60  mesh   sieve   and    shipped    in  air-tight   casks. 
Hydrated    lime :-        Study  Article   333-      Ordinary   quicklime    is 
treated   at  the  mills,   with   only  enough  water  to   slake    it  completely. 
Hydrated    lime    is  a   fine   powder   consisting   of  calcium  hydrate  and 
magnesium  oxide.      Lechanical  hydrators  are   used   and   the  product   is 
under    strict  control.      The   tensile   and   compressive   strengths   of 
hydrated    lime  mortars  are   higher  than  those   of  the   corresponding 
quicklime  mortars,      Hydrated    lime  mortars,   besides  having  greater 
strength,    set  more  quickly  and   shrink  less  than  ordinary  quicklime 
mortars,   but   the   latter   excel   in  plasticity,    sand-carrying  capacity, 
and   yield. 

The   consumer  must  pay   freight   on  a  considerable  amount   of 
water  when  he   bays   hydrated    lime,    out   in   its  use  the   danger   of  burn- 
ing  or   drowning  and   the  time   and    laoor   required    in  the    slaking  of 
quicklime   are   eliminated. 

The   principal  use    of   hydrated    lime  as  a   structural  material 
is    in  portlarid   cement  mortars   and   concretes. 
Testing   of   limes:-          Read   Article   384. 

Uses   of   lime:-     Read   Article  §86*      Besides  the   uses  mentioned    in 
this  article    lime    is  used   for   the  manufacture   of  sand-lime  brick, 


Civil  Bnfer-8.  ^ssigruusnt    11.  .Fags    7. 

and   of  glass,  paints  and   pf.per.        It   is  also  used   as  c.  fertiliser 
and    in  the   tanning   of   leather- 

Hydraulic    liiue   and   grappier   cement:-  Read  Articles   387     and   388. 

liyoraulic    line  was  used   for    structural  purposes  before  the    superior 
natural   and   port  land   cements  were    introduced.      Its  use  at  the 
present   ti;Tie    is   limited. 

The   raw  material   is  a   siliceous   or   argillaceous   limestone. 
The    ideal   stone    is   one   that   has    sufficient  free    lime   remaining  after 
calcination  to  disintegrate   the   clinker    by   its  disruptive  action 
•when  slaked.      During  calcination  the   silica  combines  with  the   lime 
to  form  lime    silicate  which  gives  the   product   its  hydraulic  proper- 
ties.     The   slaking  of  hydraulic    lime,   as   in  the  case   of  hydrated 
line,    is  done   by  the   producer.      The    lumps  that  are   not  disintegrated 
during  the    slaking  process  do  not  contain  a   sufficient  amount   of 
lime    or  they  are   under-burned.      These   lumps  have   been  called   grappiers 
When  they   contain   sufficient   lime    silicate  they   are  finely  ground 
and   marketed   as   grappier   cement.      Lafarge   cement,   noted    in  Article 
388,    is  a   grappier   cement. 

The   properties   of  hydraulic    lime   are  very   low   in  value,  when 
compared   to  those   of  port land   cement. 

GYPSUM 

Introduction:-       Read  Article   389-          Wall  plasters  and  plaster   of 
Paris,   as   noted    in  this   article,    are  made   of  gypsum.      It   is  also 
used    in  the  manufacture   of  precast    structural  products  and   struc- 
tural members  cast   in  place.        Gypsum  is  added   to  portland   cement 
to   retard    its   set,   a ad   raw   gypsum,   which  is  known  as    land-plaster, 


Civil  En§i--8.  Assignment    11.  Page  8. 

is   used   as  a  fertilizer. 

Occurrence:-       Read  Article  320.     Gypsum  is  a  common  mineral;   its 

iiios-c   distinguishing  characteristic    is   its  extreme    softness.      The 

pure   material  consists   of  approximately  32.6$  lime,   46.5^  SO*     a^d 

20.9$     water.      It    is  a  neutral   substance;     that   is,    it    is   neither 

acio   nor    as. sic. 

Calcined   gypsum;-       Read  Article   392.      Calcined   gypsum  is  known 

by  many  name 3,    some   of  which  are   derived   from  the   purpose   for  which 

it   is   used,  as  dental  plaster,   molding  plaster,   casting  plaster 

and   potter's  plaster.      These  materials  are   all  calcined   gypsum  and 

differ   only   in  the  tirae   of  set,  which  has  been  regulated.      The  most 

common     name  for  calcined   gypsum  is  plaster   of  Paris. 

Calcined   gypsum  is  produced  by  heating  finely  ground   raw 
gypsum.      The  product   is  made   in  kettles  which  hold   from  2  to  20 
tons.          During  the   heating  process  the   gypsum  is  continuously 
stirred    oy  a  power -driven  paddle.      The  water   held   in  chemical  com- 
bination is  driven  off  as   steam  which  fluffs  up  the  whole  mass  and 
makes    it   appear  to   boil.      It   settles  down  to   its  normal  volume 
when  the   boiling  action  ceases;      this  usually  te.Kes   about  an  hour 
for   a  kettle   full   of  material.      The   exact  time  depends  upon  the 
charge   and   the  temperature.        The   product    is  calcined   gypsum  but 
to  the   operator    it   is   known  as   first-settle   stucco.      It    is  partially 
dehydrated   gyps am,  with  chemical  formula  usually  written  CaS04* 1/2 
HgO  Calcined   gypsum,  when  mixed  with  water,    sets  and   hardens 

rapidly  to  form  a  material   identical  with  the    original  gypsum 


Civil  Er.£i'-8.  Astsi^iiirsnt    11.  Page   9. 


.      The    setting   of  n.c?rae.l  calcined   gypsura  occurs   in  from  5 
to   10  minutes.     When  used   for   dental  purposes  the   time   of   set   is 
accelerated    but  when  used   as  a  wall  plaster   the  time    of   set   is 
retarded.      Some  wall  plasters  are  regulated   so  as  to  set   in  about 
20  minutes  while   in  others  the   set   is  retarded  to  aoout   six  hours. 

Set  gypsum,  when  the   normal  calcined  gypsuia  is  used,   has  an 
approximate   eompressive   strength  of   1,500  Ib.    per    sq.    in.    and   a 
tensile   strength  of  400  Is.    per   sq.    in.      bince  moisture   in  the 
specimen  decreases    its   strength,   the  maximum  value   can  be   develop- 
ed .  only  when  the  material   is   dry.      The   amount   of  mixing  water   has 
a   dec  iced   effect   on  the    strength  of   set   gypsum.      For  maximum 
strength  the    least  possible  amount   of  mixing  water    should   be   used. 
Gypsum  wall  plaster:-          Read   Article   393-      It  has  been  estimated 
that  three-quarters   of  the   gypsum  mined    is  made    into  wall  plaster., 
Calcined   gypsum   is  the    simplest  wall  plaster.      It   is  not  used   pure 
but    is   added  to   lime  paste. 

Calcined   gypsum  is  not  plastic   and  therefore   is  difficult 
to   spread  with  a  trowel.      It   has  become   the   practice   to  add   aoout 
fifteen  percent   of  clay   or   rvydrated    lime  to   it  at  the  mill.      A 
retarder   is  added   to  the  material   so  that    it  will   set   in  from  one 
to   six  hours.      This  product    is  known  as   hard  -wall  plaster   on  the 
eastern  market,    but    in  the  west,   the   same  material   is  called 
cement  plaster. 

The   principal  disadvantage    of  calcined   gypsum  when  used   pure 
is    its    lack  of  plasticity.      By  proper  methods    of  manufacture,  which 


Civil  Er.gr -8.  Assignment   11.  page   10. 

are   explained    in  an  article,   PLASTIC  GYPSUJa  &ADE  POSSIBLE  BY  A 
NEW  METHOD,    by  w.E.  Emley,   Engineering  News-Refcord   86,    1U23,    June 
3.6,    19P1,    it  can   be  mace   as  plastic   as    lime.        Fine   grinding  of 
ctlcined  gypsum  liberates  the  water   of  crystallization  just  as   heat- 
ing does.      If  the   escape   of  the  water   is  prevented,    so  that  the 
finely  ground   gypsum  contains  the  water   of  crystallization,    it 
produces  not   only  a  more  plastic  and   slower   setting  material  but 
also  a   stronger   one.      If  the  water   of  crystallization  is  allowed 
to  escape  during  the   grinding  process  the  product  will  be  the 
soluble  anhydrite  which  rapidly  reabsorbs  water     from  the  air  and 
reverts  to  the  calcined   gypsum.        There   is  no  advantage   in  fine 
grinding  under   such  conditions.      The  new  plastic -gypsum  is  very 
stable;      it  has  been  exposed  to  air  for  four  months  without 
apparent  detriment  to  its  plasticity. 

Second -settle  calcined   gypsum:-      If  calcined   gypsum  is  properly 
heated    it  will  appear   to  boil  and    subside   just  as  the   raw  gypsum 
did  when   it  was   heated.      During  the   second    uoiling  all  the  water 
held    in  chemical  combination  is   driven  off  so  that  CaSO^  remains; 
this    is  anhydrous  calcium  sulphate.      To  distinguish  between  this 
product   and   the   natural  anhydrite  which  has  the   same   formula   but 
very  different  physical  properties,   the   former   is  called    soluble 
anhydrite.          The  mineral  anhydrite    is   quite   inactive.      It   is 
weeks   before    it   combines  with  water  to  form  set  gypsum.      The   sol- 
uble  anhydrite    sets  more   rapidly  than  the  calcined   gypsum  and 
makes  a  harder  and   stronger    set   gypsum.      The   soluble  anhydrite   is 
not    stable   -   it  readily  absorbs  water   from  the   air   to  form  the 


Civil  Engr-8.  Assignment  11.  Page  11. 

calcined  gypsum;  but  because  of  its  greater  strength  it  is  used 
at  the  mill  to  make  precast  products.  The  material  cannot  be 
shipped  or  stored. 

Hard  finish  plasters:-  Read  Article  394.   Calcined  gypsum  is  chang- 
ed to  the  soluble  anhydrite  at  aoout  500  degrees  Fahrenheit.  The 
latter  material  is  converted  into  the  natural  or  mineral  anhydrite 
by  prolonged  heating  or  higher  temperatures.   In  spite  of  its  slow 
set,  the  natural  anhydrite  is  used  in  Europe  as  a  floor  surface. 

Keene's  cement  is  described  in  the  text  on  page  369.   It 
sets  more  slowly  than  calcined  gypsum  and  makes  a  harder  surface. 
Gypsum  building  products:-   Read  Article  395.   One  variety  of 
gypsum  tile,  which  is  generally  used  for  partitions,  is  made  at  the 
mill  with  calcined  gypsum  to  which  aoout  b%  of  wood  fiber  has  been 
added.   This  variety  is  made  cellular  like  the  clay  partition  blocks 
shown  on  page  2S3.   The  usual  dimensions  are  12  by  30  inches  with 
thicknesses  varying  from  2  to  8  inches. 

Roofing  tile  must  be  stronger  than  partition  tile.   They  are, 
therefore,  made  of  second-settle  calcined  gypsum  and  are  frequently 
reinforced  with  steel  rods  and  v; ire -mesh.   Standard  roof  coverings 
are  used  to  protect  gypsum  tile  from  the  weather.   Kiln-dried 
gypsum  products,  like  roofing  tile,  gain  their  full  strength  within 
a  few  hours. 

Gypsum  plaster  board  is  made  in  laminations  -  a  thin  layer 
of  calcined  gypsum  between  layers  of  paper.   It  is  used  as  sheet- 
lath  as  a  base  for  plaster.   The  gypsum  usually  contains  a  wood- 
fiber  to  decrease  its  brittleness.  Gypsum  wall  board    is 


Civil  En^r-8,  Assignment   11.  Page    12. 

similar  to  the  plaster  "board.      In  the  case   of  the   latter,  however, 
plaster   is  apoiieo  to  the   surface  wnile  the  wall  "board  has  a 
sraoc-h  surface  and   is  not  plastered,   tut  forms  the  finished  wall. 
Saeetrock  is   the  trace   name   for  a  gypsum  -flail- board   now  bsing 
widely  advertised. 

otractural  members   such  as   roofs  can  be   poured   into  place 
just  as   in  cemenc-corcrete   construction.      On  page   4   of  the  ad- 
vertising,  section  of  the   March  23,    1922    issue    of  the  Engineering 
News-Record,    is  an   illustration  in  which  the   roof   of  the  National 
Tube  Company's  pirnc,  at  Lorain,    Ohio,    is  being  poured  with  gypsum. 
Structural  gy?sun  gains   strength  rapidly;   the   forms  are  taken  off 
the  day  after  the   gypsum  has  been  poured.     The  compressive   strength 
is  affected  by  several  variable  factors,  the  principal  ones  being 
the  amount   of  mixing  water  used  and  the  amount   of  aggregate   - 
send   or  wood-fiber.     Prolonged  moisture  reduces  the   strength  of 
structural  gypsum.     An  average  value   of  the  compressive   strength 
is    1,500   lb.    per   sq.    in.      It  weighs  about  80  lb.    per  cu.    ft.    and 
has  a  modulus   of  elasticity   of  about   1,000,000  Ic.    per   sq.    in. 
Magnesia  cement;-       This  material   is  not  discussed    in  the  text. 
It    is  made   by  mixing  magnesium  oxide  v;ith  a   solution  of  magnesium 
chloride.      Various   aggregates   such  as,    sand,    sawdust  and  asbestos, 
are   added  to  the   cement.      It    is   sometimes  called   Sorel  cement, 
after    its    inventor,    Stanislaus   Sorei,   and   also  megnesium  oxychlor- 
ide   cement.      It    is  used   principally  as  an  interior  \vall  finish  and 
as   flooring.      In  the  East   it   is  nov;  being  used  as  an  exterior  wall 
surface. 


Civil  Engr-8.  Assignment  11.  Page  13. 

The  magnesium  oxide  is  prepared  by  calcining  and  grinding 
inagr.es it e  (^~00,).   There  are  large  deposits  of  magnesite  on  the 
Pacific  Coast.  The  more  important  deposits  which  are  being  worked 
are  in  Greece,   ItP.ly,  and  Austria. 

The  methods  of  manufacture  and  the  properties  of  magnesia 
cenents  are  being  studied  by  the  U.S.  Bureau  of  Mines  and  the  Dow 
Chemical  Company,  who  operate  a  well  equipped  magnesium-oxychlor- 
ide  research  laboratory. 

The  following  notes  were  taken  from  reports  by  the  Dow 
Chemical  Company. 

The  stancarc  stucco  mix  is  1  part  calcined  magnesite  to  2 
parts  Silex  (powdered  silica)  to  5  parts  graded  silica  sand  mixed 
with  22  degree  Eaunie  magnesium  chloride.  The  strength  of  this 
material  varies  (from  various  test  results)  from  200  to  1000  Ib. 
per  sq.  in.  at  30  days.  When  placed  on  the  wall  its  average  ten- 
sile strength  is  about  500  Ib.  per  sq.  in.   Its  compressive 
strength  is  about  5  1/2  times  its  tensile  strength.   Its  modulus 
of  elasticity  is  approximately  3,000,000  Ib.  per  sq.  in. 

Standard  flooring  mix  is  5  parts  calcined  magnesite,  3  parts 
Silex,  1  part  ground  talc,  1  part  fiber  (wood  or  asoestosj  and  one 
part  color  pigment,  all  mixed  with  22?  Baume  magnesium  chloride. 
For  heavy  duty  the  following  mixture  is  used:   12  1/2%  calcined 
magnesite.,  35^  Silex,  62  1/2^,  pure  silica  sand.   This  is  also  mix- 
ed with  22  degree  Baume  magnesium  chloride,   kagnesite  makes  a 
sanitary,  resilient  floor  which  has  a  good  appearance  and  excellent 


Civil  Engr-3.  ^ssigni^snt   11.  Page   14. 

•wee.riiig  qualities.      It   is   fre<=   fron,  the   splintering  action  of  wood 
floors  and    ir   not   suoject   to  dusting  or    sanding.     By  actual  test 
it  v.as   found   to   oe  more  durable  than  linoleum. 

Most   of  the  early   literature   on  the   suoject   states  that 
cxychlcride   cements  are   disintegrated  by   continuous  wetting   or 
i;amer;=ion  in  water.      &t  the   present   time    lit   is    oelieved   that  the 
degree   of  burning  affects  the  water  resisting  properties.      Since 
oxychloride  cements  are  usec   for   exterior   stucco  it   is  evident 
that  -vhe.n  properly  designed  and  applied  they  are  water  resistant. 
Commercial  magnesium  cements  can  be   secured  which  make  a   stucco 
that    is  practically  water   resistant. 


Ci'.'il  Engr-S.  Assignment  11.  page  15. 

QUESTIONS 

1.  What   is   slaked   lime? 

2.  Vifiiat  precautions  must  be  ta&en  in  slaking   lime? 

3.  Can  lime  mortar   be  used  uncler  water? 

4.  What   is  doloinitic   lime? 

5>      HOV?   is    .lydrated   lime  made? 

6.  Outline  the  manufacture    of  calcined   g,ypsum« 

7.  What  are   the  general  uses   of  gypsum  as  a   structural  material? 
What  factors  affect  the    strength  of  gypsum? 

9.  How  does  plastic -gypsum  d lifer  from  ordinary  calcined   gypsum? 

10,  irVhat   is  magneaiua-oxychlorid*  cement?     Whet   is   it  used  for? 


UNIVERSITY  OF  CALIFORNIA  EXILNSION  DIVISION 

Correspondence  Courses 
Materials   of  Engineering  Construction 

Assignment   12. 
Civil  Engr-gA  Professor  C-T-    Wiskocil 

TESTING  OF  HYDRAULIC   CEL-£NTS 

Necessity  for  testing  cenent:-       Read     carefully  that   part   of  Article 
396  which   is  given  on  page   371,   and  then  Article  443.      The  third  para- 
graph  on  page   371   is  v-sry   important   -  study   it.      The   physical  tests 
are  the  most   important  and  are  made  for  the  purpose   of  comparing 
the  given  cement  with  a   standard  -which  has  been  adopted  after   long 
experience.      The   results  of  laooratorj   tests  do  not   represent  the 
properties   of  the  material  under  v/ or  king  conditions  but  they  are   of 
relative  value  when  compared  -.vrth  test  results  of  cements  that  have 
been  found   satisfactory   in  practice. 

Standard  ^specifications   ior  portland  cement:-     Read  the   remainder 
of  Article   396.      Study  the   perts  narked    II  and  V,    because  they  are 
important.     Be  acle  to  name  the  various  tests   and   give  the   standard 
requirements.     These   specifications  are   used   throughout  the  United 
States.      The   United    States  Government    specifications  are   substanti- 
ally the   same. 

STANDARD  TESTS 

Samp 1 ing : -       Read  Articles  397  to  401   inclusive.      The   important 
thing  to  be   remembered    in   selecting  a   sample    of  cement   is  that   it 
should  be   fairly  representative.      This   is  -well  emphasized   in  the 
text,   together  vith  the   importance   of  proper   storage   and  mixing. 


Civil  Engr-8.  Assignment  12..  Page  2. 

in  the  quartering  process  described  in  Article  401,  it  is  the  usual 

re\®Or 

practice  to^dibie&aid  opposite  quarters  of  the  pile  and  combine  the 
remaining  quarters  which  are  again  mixed  and  divided  into  quarters. 
The  process  is  repeated  until  the  amount  remaining  gives  the  size 
of  the  sample  desired. 

Chemical  analysis:-   Read  Articles  402  and  407.   Since  the  chemi- 
cal tests  are  relatively  unimportant,  omit  Article  403  to  406 
inclusive. 

Specific  Gravity:-.  Read  Articles  408  and  448.   This  test  is  not 
very  significant.  For  that  reason,  as  indicated  in  the  specifi- 
cations on  pags  372,  it  is  made  only  when  specifically  called  for. 
Adulterants  such  as,  Slag,  limestone,  and  natural  cement  could  be 
present  in  quite  appreciable  amounts  before  the  specific  gravity 
would  be  noticably  affected.   The  specific  gravity  test  does, 
however,  indicate  the  degree  of  seasoning.   Cement  clinker  and 
ground  cement  both  absorb  water  and  carbon  dioxide  from  the  air, 
causing  the  specific  gravity  to  decrease.   The  loss  due  to  season- 
ing is  regained  upon  ignition  of  the  sample. 

Low  specific  gravity  may  be  the  result  of  adulteration. 
It  is  also  indicative  of  the  degree  of  seasoning.   Since  seasoning 
is  desirable  in  portlar.d  cements  a  value  below  3.10  for  the  spe- 
cific gravity  should  not  be  cause  for  rejection  without  some  ,*•  f 
definite  reason  based  on  the  history  of  the  cement  in  question. 
Fineness:-  Read  Articles  409  to  412  inclusive,  and  Article  447. 
The  paragraphs  nar::ed  34,  35,  and  36,  in  Article  409,  are  the  most 


Civil  Engr-8  Assignment   12.  Page  3 


important.      The   standard  method^  of  hand  sieving   is  given  preference 
over  mechanical  methods^      Since  the  eand  carrying  capacity  and 
comprcssive    strength     of  mortar  and  concrete  are   increased  by  fine 
grinding  it   is  desirable  for  the  manufacturer  to  obtain  the 
maximum  degree  of  fineness  compatible  with  reasonaole  manufactur- 
ing costs.     Fine  grinding  decreases  the  time   of  set. 

Fine  cements  itfill  leave  a  residue   of  about  2f0  on  a  No.    200 
sieve  while  those   of  average   fineness   leave  from  10  to  15^. 

Article  412   is  relatively  unimportant.      The  air  analyser 
developed   by  the   united    States  Bureau  of  Standards,  mentioned   on 
page   381,   has   proved  to   &e  ver^    {satisfactory   in  separating   into 
smaller   sizes  cement  which  passes  the  No.   200  sieve. 
Liixing   oi   cement   paste  and   normal  consistency:-     Read  Articles413 
to  418   inclusive       The  making  of  cement  paste  and  mortar   is  of 
importance   in  the   laboratory  in  which  test   specimens  are  prepared. 
Tbe   cement  paste   is   useo    in  the   determination  of   soundness  and 
the  time   of   set.      Cement  mortar   is  made   into  briquettes  for  the 
tension  test.      In  order  to  ootain  results  comparable  to  those 
jiven  in  the  text  the  cement  paste  and  mortar   snould  be  made   in 
strict  accordance  with  the  directions   in  the  text.      In  a  general 
course   in  iiA-IER LaLS  these   directions  are   relatively  unimportant. 

The  plasticity    or  consistency,  as   it   is  called   in  the  text, 
affects  the   strength  and   also  the  time    of   set.      It    is  necessary, 
therefore,   to  have  cements  tested   ur.cer  tie   same   conditions  ae 
those  under  which  the    stancarc   tests  were  made*      This   is  ac- 
complished   by  having  the   cement  paste   of  a  given     plasticity  as 


Civil  Engr-8.  Assignment  12.  Page  4. 

determined  in  a  specified  manner  with  the  Vicat  apparatus  illus- 
trated on  page  383.   This  determination  is  of  importance  only  in 
the  laboratory.  A  cement  paste  is  of  normal  consistency  when  the 
rod  of  the  Vicat  apparatus,  which  weighs  300  g.  and  is  1  cm.  in 
diameter,  sinks  10  ens.  into  the  paste  in  1/2  minute  after  being 
released.  This  method  is  very  satisfactory  -  but  only  for  neat 
mixtures.  The  amount  of  water  to  be  used  for  sand  mixtures,  in 
the  standard  tension  tests  is  given  in  the  table  on  the  top  of  page 
384.  Articles  417  and  418  are  not  important. 

Soundness:-    Read  Articles  419  to  424  inclusive  and  Article  444. 
Soundness  is  the  most  essential  property  of  cement.   The  ability  of 
a  cement  to  develop  a  high  degree  of  strength  is  of  no  value  if  it 
is  not  able  to  withstand  the  disintegrating  effects  of  the  atmosphere 
•when  it  is  finally  placed  in  the  structure,  tyhile  the  conditions 
in  this  test  are  more  severe  than  those  to  which  the  cement  will  be 
subjected  when  it  is  put  in  use,  the  results  are,  nevertheless, 
quite  satisfactory  in  indicating  the  durability  of  a  given  cement. 
The  illustrations  on  page  386  show  par^s  that  have  failed  to  pass 
the  soundness  test.  Articles  421,  422,  and  423  are  not  important. 
Time  of  setting;-     Read  Articles  425  to  427  inclusve  and 
Article  446.   The  rapidity  with  which  a  cement  sets  is  a  criterion 
of  its  adaptibility  under  given  conditions  of  use.   In  some  types 
of  construction  it  might  be  desirable  to  have  a  cement  which  would 
set  quickly.   In  other  circumstances,  where  it  is  impossible  to 
place  the  concrete  without  delay,  it  is  necessary  to  have  a  slower 


Civil  Engr-8.  Assignment  12.  Page  6. 

setting  cement.  The  influence  of  the  temperature  and  the  amount 
of  mixing  water  used  ere  explained  on  pages  327  and  328  in  the 
text.  The  tables  are  given  in  a  previous  assignment  but  it  is 
desirable  to  review  the  general  affect  of  these  variables  at  this 
time.  Paragraphs  marked  48  and  50  in  Article  425  are  the  most 
important. 

Tension  test:-  Read  Articles  428  to  439  inclusive,  and  Article 
445.   The  standard  tension  test  is  made  on  briquettes  of  sand 
mortar.  The  proportions  of  the  mortar  are,  one  part  cement  to 
three  parts  standard  sand,  mixed  with  the  amount  of  water  deter- 
mined by  the  normal  consistency  test,  according  to  the  table  on 
page  384.  A  special  sand,  described  in  the  paragraph  marked  52 
on  page  391,  is  used. 

Study  Articles  429  and  431.  The  latter  article  explains 
that  the  stress  across  a  briquette  under  test  is  not  uniform. 
This  non-uniformity  of  stress  in  a  test  specimen  is  an  undesir- 
able feature  in  a  tension  test.   Since  the  modulus  of  elasticity 
of  mortar  varies  with  age,  the  temsion  tests  at  various  ages  do  :. 
not  give  a  true  indication  of  the  variation  .in.  the  average 
tensile  strength  of  the  material.  This  is  not  important  in  the 
standard  tests  here  described  but  it  is  important  in  research 
problems.   In  such  work  the  compression  test  on  cylindrical 
specimens  is  more  generally  used. 

Articles  432,  433  and  434  ere  not  important.  • 
Storage  of  test  specimens :-   Test  specimens  are  stored  in 
a  moist  closet,  as  described  in  Article  441,  for  24  hours.  Alter 


Civil  Engr-8.  Assignment  12.  Page  7. 

that  they  are  removed  from  the  molds  and  immersed  in  water.  As 
stated  in  Article  440,  it  is  important  that  the  temperature  of  the 
air  in  the  moist  closet  and  the  temperature  of  the  water,  in  which 
test  specimens  are  stored,  should  be  as  nearly  70  degrees  Fahren- 
heit as  possible. 

Miscellaneous  methods  of  testing  cements :~     Read  Articles  449  to 
453  inclusive.  All  of  these  tests  are  unimportant.   In  most  re- 
search problems  it  is  frequently  necessary  to  devise  new  methods 
of  testing,  and  special  apparatus. 


Civil  Engr-8.  Assignment   12. 

QUESTIONS 

1.  Name  the  standard  physical  tests  for  portland  cement. 

2.  Give  the  standard  requirements  for  the  tests  given  in  (1). 

3.  What  is  the  relative  importance  of  the  tests  given  in  (1)? 

4.  What  constitutes  grounds  for  rejection  of  a  biven  cement? 

5.  Explain  the  quartering  process  as  applied  to  the  sampling 
of  cement. 

6.  HOW  is  unsoundness  of  cement  usually  manifested? 

7.  What  is  meant  by  the  tsrm"normal  consistency  of  cement'*? 

8.  Why  is  it  necessary  to  determine  the  normal  consistency? 

9.  What  are  the  two  methods  used  to  determine  the  t,ime  of 
setting? 

10.  What  are  the  reasons  for  the  tension  test  of  cement? 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Coi respondence  Courses 
Materials  of  Engineer  ing  Construction 

Assignment  13. 

Civil  3ngr-8A.  Professor  C-T-  Wiskocil 

C  ONC9ETE  AgGKES  ATE  S 

Int  rod  action:-   Study  Article  454;  it  is  important.   There  is  a 
growing  tendency  among  engineers  to  specify  the  consistency  and 
strength  requirements  for  concrete  on  various  portions  of  a  job, 
and  to  give  the  contractor  an  opportunity  to  furnish  concrete  of 
required  strength  according,  to  his  own  methods. 

DEFINITIONS 

Study  Articles  4£5  to  464  inclusive.   All  the  terras  used 
in  the  discussion  of  mortar  and  concrete  are  defined  and  it  is 
necessary  trat  they  "be  thoroughly  understood. 

Mortar :-  As  defined  in  Article  455,  mortar  is  essentially  a  mix- 
ture of  fine  aggregate,  which  is  usually  sand,  cement  and  water. 
Concrete:-  Concrete  is  defined  in  Article  456.   It  consists  of  a 
large  bulk  of  inert  materials  in  a  finely  divided  state,  bound  to- 
gether "by  a  comparatively  small  amount  of  cement.   The  amount  of 
water  used  in  mix.ing  the  ingredients  is  of  great  importance.   Con- 
crete is  frequently  named  according  to  the  kind  of  aggregate  used, 
as  crushed-stone  concrete,  gravel  concrete,  cinder  concrete  and 
rubble  or  cyclopsan  concrete. 

Cement:-  Cement  has  been  previously  defined.   In  this  text  only 
Portland  cement  concrete  is  discussed.  Bituminous  concrete  is 
used  principally  for  the  surfacing  of  roads  and  highways. 


Civil  Engr-8.  Assignment  13.  Fage  2. 

Aggregate:-  As  stated  in  Article  453  aggregates  are  divided  by 
the  1/4  inch  screen.  TLhose  that  pass,  are  classed  as  fine 
aggregates  and  those  that  are  retained  are  called  coarse  aggre- 
gates.  Sand  is  tLe  principal  fine  aggregate,  while  crushed  stone 
and  gravel  are  the  predominating  coarse  aggregates. 
Silt:-   See  Article  459.   Silt  is  usually  considered  as  the  fine 
material  which  passes  a  No.  200  sieve.   In  rich  mixtures  silt  is 
an  undesirable  ingredient  and  is  classed  as  an  impurity.  A  cer- 
tain amount  of  silt,  however,  will  benefit  or  improve  the  strength 
of  lean  mixtures. 

Specific  Weight :-   This  term  is  defined  in  Article  460.   It  is 
the  weight  in  pounds  of  a  definite  volume,  usually  specified  as 
one  cubic  foot.   Since  there  are  no  standardized  methods  for  its 
determination  it  is  necessary  to  state  the  conditions  under  '-vhich 
it  is  determined.  The  moisture  content  as  shown  in  Figure  5  on 
page  418  is  an  important  factor  in  the  case  of  fine  aggregates. 
For  coarse  aggregates  the  shape  and  size  of  the  measuring  oox 
affects  the  specific  -wei^iTt.   The  method  of  filling  the  measure  or 
of  compacting  the  aggregates  into  it  are  important  for  both  fine 
and  coarse  aggregates. 

Voids:-  Voids  as  described  in  Article  461  are  the  spaces  between 
the  particles  of  aggregate.   The  vcid  space  is  alv.-ays  expressed 
as  a  percentage.   The  two  methods  of  determining  the  void  space 
in  an  aggregate  are  described  in  this  article.   There  is  a  direct 
relation  between  the  specific  weight  and  the  percentage  voids. 


Civil  Fn^-r-3  Assignment  13.  page  3. 

method  of  determining  the  percentage  voids  the  first  term  in  the 
numerator  gives  the  weight  of  a  cuoic  foot  of  solid  material,  the 
second  term  gives  the  actual  weight  of  a  cuoic  foot  of  the  aggre- 
gate; the  difference  is,  therefore,  the  amount  of  void  space, 
which,  wnen  divided  by  the  first  term,  gives  the  percentage  void 
spaces. 

Mechanical  analysis-.-   The  first  paragraph  in  Article  462  and 
the  second  paragraph  on  page  411,  which  describes  the  method  of 
making  a  mechanical  analysis,  are  the  most  important.  All  scien1- 
tific  methods  of  Delecting  and  proportioning  aggregates  are  based 
on  mechanical  or  sieve  analyses.   The  amounts  passing  or  retained 
on  each  sieve  in  the  series  are  expressed  in  percentage  and  usually 
put  in  the  form  of  a  diagram  similar  to  that  on  page  417. 
Yield;-  The  customary  method  of  determing  yield  is  described  in 
Article  463.  The  minimum  yield  obtained  by  varying  the  proportions 
of  given  aggregates,  but  keeping  the  proportion  of  cement  to  total 
aggregate  cor.ste.nt,  is  used  as  a  means  of  proportioning  concrete 
aggregates.  This  method  will  be  discussed  in  the  next  assignment. 
See  page  429.   Yield  is  frequently  determined  in  investigations  on 
concrete.   It  is  taker,  as  the  ratio  of  the  volume  of  concrete  t2 
produced  by  a  given  volume  of  mixed  aggregates.   The  volume  of  the 
concrete  is  measured  when  the  specimens  are  removed  from  the  molds. 
For  1  to  6  concrete  the  yield  is  usually  about  unity  (1.0)  but 
for  rich  mixtures,  one  part  cement  to  two  parts  sand,  it  may  in- 
crease to  1.3.   For  lean  mixtures,  such  as  1  to  9,  it  may  be  con- 
sidered as  being  unity.   Additions  of  hydrated  lime  cause  an  in- 


Civil  Enbr-8.  Assignment  13.  •    page  4. 

crease  in  the  yield  of  the  us^al  concrete  mixtures. 
Density:    As  defined  in  Article  464,  density  is  the  ratio  of 
total  solid  material  in  the  concrete  to  its  volume.   The  volume  of 
the  concrete  is  determined  after  it  has  hardened.   It  is  one  minus 
the  void  space  -when  the  latter  is  expressed  as  a  ratio  of  voids  to 
total  volume.  The  density  of  1  to  5  mortars  is  about  .71,  while 
for  1  to  5  concrete  having  aggregates  up  to  1  1/2  inch  it  may  in- 
crease to  aoout  .S3    Density  is  affected  by  the  richness  of  the 
mix  anc  the  amount  of  water  used  in  the  mixing - 

CH^RACriRISTICS  AND  PROPERTIES  OF  FINE  AGGREGATE 
Importance  of  good  aggregate   is  emphasized  in  Article  465.  The 
last  sentence  in  that  article  is  important.   What  it  says  is  this: 
the  best  criterion  for  the  suitability  of  a  given  aggregate  for 
concrete  is  actually  to  maKe  some  concrete  with  the  aggregate  and 
test  it.   This  means  thai  the  value  of  a  fine  aggregate  cannot  be 
determined  by  a  mortar  test. 

Sampling  aggregate:-   Read  Article  466.   Considerable  judgment  is 
required  in  securing  a  representative  sample  from  a  sand  or  gravel 
deposit.   Care  is  necessary  in  sampling  material  that  is  piled. 
This  is  intimated  in  the  last  paragraph  in  the  article. 
Requirements  for  fine  aggregate:-   Study  Article  467.   The  last 
sentence  in  the  article  is  particularly  important.   Note  that  the 
sharpness  of  sand  grains  is  not  essential.   At  one  time  all  specifi- 
cations stated  that  the  sand  grains  should  be  sharp.  When  it  is 
necessary  to  use  an  untried  sand,  which  appears  to  have  a  satis- 
factory grading  and  hard  grains,  its  suitability  can  be  quickly 


Civil  Engr-8.  Assignment  3.3  Page  5. 

estimated  by  the  color  test  described  at  the  bottom  of  page  4J.5. 
The  presence  of  organic  matter  which  might  prevent  the  setting  of 
the  cement  can  be  readily  detected  by  this  method.  On  important 
r.'ork  an  untried  sand  should  not  be  used. 

Composition  of  particles;-   Read  Article  468,  and  study  the  last 
paragraph,  '.vhich  gives  a  list  of  some  of  the  objectionable  minerals 
in  fine  aggregates  - 

Impurities :-   Ltudy  Article  469.   A  sufficient  number  of  tests 
have  been  made  tc  substantiate  the  statements  made  in  the  first 
paragraph  regarding  clay.  From  the  discussion  thus  far  it  is 
evident  that  strength  tests  on  the  finished  concrete  would  prove 
the  suitability  of  given  aggregates  without  tests  for  impurities. 
Gradation  of  the  sizes  of  the  particles:-   Study  Article  470  and 
the  curves  in  the  diagram  on  page  ^17.  Stone-  screenings  are  gen- 
erally not  as  desirable  as  sand  for  fine  aggregate  for  concrete, 
because  they  decrease  the  plasticity  of  the  concrete,  and  if  the 
plasticity  of  the  mixture  is  brought  to  the  desired  point  with 
water  the  strength  of  the  concrete  "will  be  decreased. 
Voids  and  specific  weight;-   Study  the  first  two  paragraphs  of 
Article  471,  and  read  the  remainder  of  the  article.   Remember  the 
general  tendency  oi  the  curves  in  diagram  5.   The  voids  in  a  satur- 
ated sand  my  be  equal  tc  or  lo^er  than  those  in  the  dry  sand. 
The  moisture  content  must  be  known  when  the  voids  are  determined. 
The  actual  amount  of  fine  sand,  containing  two  to  ten  percent 
moisture,  in  a  cuoic  foot  of  the  material  is  much  less  than  it 


Civil  Engr-8.  Assignment  13.  Page  6. 

would  be  if  the  sand  were  dry  or  saturated. 

Remember  these  average  values  for  sand:  Specific  gravity, 
2.65;  voids,  SOjfe;  weight  in  Ib.  per  cu.  ft.,  11Q. 

Mortar  tests  :-   Study  the  second  paragraph  in  Article  472  and  read 
the  remainder  of  the  article.   In  comparing  mortars  of  given  pro- 
portions it  is  necessary  to  mix  them  so  that  they  have  the  same 
consistency.   The  consistency  of  sand  mortars  is  not  so  easily  de- 
termined as  that  of  neat  cement  paste.  The  Vicat  apparatus  is  not 
satisfactory  and  other  methods  must  be  resorted  to;  one  of  them  is 
outlined  on  page  420.  Compressive  tests  on  cylindrical  specimens 
are  cmost.  satisfactory.  The  molds  for  these  specimens  are  2  inches 
in  diameter  and  4  inches  long. 

CHARACTERISTICS  AND  PROPERTIES  OF  COARSE  AGGREGATE 
Requirements  for  coarse  aggregate  :-    Head  Article  473.  Roughly 
cubical  or  rounded  stones  are  preferable  to  those  of  other  shapes. 
The  use  of  the  different  stones  as  concrete  aggregate  has  been  given 
in  a  previous  assignment. 

Characteristics  and  properties  of  broken  stone  :-   Read  Article  474. 
For  unreinforced  concrete  the  usual  size  of  coarse  aggregate  varies 
from  1/4  to  1  1/2  inches.   The  maximum  size  of  particle  is  smaller 
for  reinforced  concrete,  usually  being  limited  to  that  which  will 
pass  through  a  1  inch  ring.   If  the  amount  of  reinforcement  is 
large  and  closely  spaced,  as  was  the  case  in  the  concrete  ships, 
the  maximum  size  of  aggregate  is_tstill  smaller. 

Table  2  on  page  423  is  interesting  in  that  it  shows  the  effect 


Civil  Engr-8.  Assignment  13.  page  7. 

of  jarring  and  vibration  caused  oy  hauling,  on  the  specific  weight 
of  crushed  stone.  This  increase  may  be  expected  in  the  case  of  any 
course  aggregate  as  was  intimated  under  the  discussion  on  specific 
weight. 

The  diagram  on  the  upper  part  of  page  423  will  be  referred 
to  when  proportioning  is  discussed  in  the  following  assignment. 
Characteristics  and  properties  of  gravels ;-  Read  Article  475. 
Gravel,  when  properly  graded  and  otherwise  satisfactory  in  regard 
to  absence  of  impurities  and  hardness  of  material,  makes  an  ideal 
coarse  aggregate  for  concrete. 

Broken  stoae  and  gravel  compared:-  Study  Article  476,  Either  class 
of  aggregate  may  "be  perfectly  satisfactory  and  neither  can  be  said 
to  be  entirely  superior  to  the  other. 

Miscellaneous  aggregates  :-    Read  Article  477.  During  the  develop- 
ment of  the  concrete  ship  various  light-weight  aggregates,  such  as 
crushed  brick,  slag,  volcanic  scoria  and  puarnice,  were  used.  The 
aggregate  finally  adopted  was  a  specially  burnt  clay  or  shale  which 
was  full  of  nonconnecting  cells  so  that  it  made  a  strong  aggregate 
of  light  weight.   It  was  crushed  to  two  sizes,  the  coarse  ranged 
from  1/2  to  3/16  inches,  and  the  fine  passed  a  screen  with  3/16 
inch  round  openings.   The  concrete  was  rich,  being  made  in  the  pro- 
portions of  1  part  cement  to  2  parts  total  aggregate.   In  addition 
a  special  fine -ground  cement,  9Q%  passing  the  No.  200  sieve,  was 
used.   The  concrete  weighed  about  118  Ib.  per  cu.  ft   instead  of  the 
usual  150  Ib.  per  cu.  ft.  of  ordinary  concrete.    Its  strength  was 
from  3,500  to  5,000  Ib.  per  sq.  in.  in  28  days.   It  was  necessary 


Civil  Eagr-8.  Assignment    13.  Page   8. 

to  make   the  concrete  rich   in  cement  because,    in  order  to  pour   it 
in  thin  sections  with  heavy  reinforcement   it  had   to  be  very  wet.      A 
sl^mp  of  9   inches  was  specified. 

The   artificial  aggregate  was  essentially  a  bloated  brick. 
It  ras  '.nade   of  basic   clay   or   shale  which  when  subjected  to  a  tem- 
perature  of  aoout  2,000  degrees     becomes  plastic  and   sears   over   on 
the    surface.     The  coating  which   is  formed  retains  the  gases  gener- 
ated by  the  decomposition  of  the  contained  chemicals.     This  expand- 
ing gas  blows  the  cla^   full  of  cells   and  bloats   it  to  several  times 
its   original  volume. 


Civil  Engr-8.  Assignment   13.  Page   9. 

QUESTIONS 

1.  What  is  concrete? 

2.  Dsfine  density  as  applied  to  concrete. 

?.  How  is  the  void  space  in  concrete  aggregates  determined? 

4.  What  is  the  relation  between  the  voids  and  the  density  of 

concrete  V 

5.  What  is  the  value  of  the  mortar  test  in  determining  the  suit- 
ability of  a  given  se.nd  as  a  fine  aggregate  for  concrete? 

6.  What  is  the  use  of  the  so-calied  color  test? 

7.  How  7;ould  the  proportions  of  a  mortar  be  affected  if  a  damp 
sand,  say  one  having  aoout  6%  moisture,  and  the  cement  were 
proportioned  by  volume? 

8.  What  are  the  principal  requirements  for  a  coarse  aggregate  for 
concrete? 

9»  Compare  the  merits  of  gravel  and  broken  stone  aggregates. 

10.  Name  some  aggregates  other  than  stone  and  gravel  that  are  used 
in  the  making  of  concrete. 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 
Civil  Engr-8-A-  Professor  C-T.  Wiskoci 1 

Assignment  14. 
PROPORTIONING  OF  CONCRETE 

The  principles  of  proportioning:-    Study  Article  478.  The 
statements  made  in  this  article  are  a  summary  of  the  discussion  of 
strength  and  permeability  of  concrete  which  will  be  taken  up  in 
assignments  16  and  17. 

Proportioning  concrete  is  a  subject  which  involves  the 
question  of  relative  costs  as  affected  .by  the  selection  and  com- 
bination of  aggregates.'  When  different  materials  which  have  differ- 
ent characteristics  are  available,  the  proportioning  involves  the 
selection  of  those  which  are  best  suited  for  the  purpose.  After  the 
aggregates  of  proper  size  and  grading  have  been  selected  it  is 
necessary  to  decide  upon  the  proportions,  or  the  ratio  of  cement  to 
total  aggregates,  so  that  concrete  of  proper  strength  may  be  made. 
The  consistency,  as  affected  by  the  quantity  of  mixing  water  used, 
must  also  be  considered.   Frequently  the  concrete  must  T*be  very 
plastic  so  that  it  can  be  poured  into  the  molds.   If  high  strength 
is  an  additional  requirement  the  concrete  must  contain  more  cement 
than  would  be  required  to  produce  the  same  strength  if  drier  con- 
crete could  be  used.   Proportioning  of  concrete  must  take  into 
account  all  of  these  factors. 

The  first  methods  of  proportioning  concrete  were  based  on 
the  theory  that  the  maximum  strength  and  impervious ness  were  secured 


:M...:,    &    •;.,'  JLilSt 


-.  <-i  •• 


Civil  Engr-3.  Assignment  14.  page  2. 


Tchei,  the  concrete  v;as  of  ma::imum  density.  According  to  these 
methods  there  *.vere  :  arbitrary  proportions,  proportions  based  on 
roics,  proportions  based  on  minimum  yield,  and  proportions  based 
on  mechanical  analysis.  The  more  recent  methods,  one  based  on 
surface  areas  of  materials  and  the  other  based  on  fineness  modulus 
ana  -water  ratio,  do  not  use  the  maximum  density  criterion.  These 
ruethods  tvill  now  be  explained  in  detail. 

The  measurement  of  proportions  :   Read  Article  47S.  The 
tendency  at  the  present  time  is  toward  greater  accuracy  in  the 
measurement  of  concrete  aggregates.  The  vheel  barrow  is  the  measur- 
ing device  in  general  use  but  automatic  measuring  scales  are  on 
the  market.  Tnese  devices  can  be  economically  used  only  on  large 
jobs.   In  the  laboratory  the  materials  are  proportioned  by  weight, 
unless  otherwise  specified. 

Arbitrarily  selected  proportions  ;-  Study  Article  480.   Con- 
crete proportions  are  usually  stated  by  volume.  A  1:2:4  mixture, 
one  part  cement  to  two  parts  fine  aggregate  to  four  parts  of  coarse 
aggregate,  is  standard.   In  this  method  it  is  assumed  that  there 
are  generally  about  50^  voids  in  the  coarse  aggregates.  The  amount 
of  fine  aggregate  (sand)  specified  is,  therefore,  one  half  the 
volume  of  the  coarse  aggregate  even  though  the  cement  and  water 
used  v;ill  bring  the  resultant  mortar  to  more  than  50^  of  the  vol- 
ume cf  the  coarse  aggregate.   The  ratio  of  volume  of  cement  to 
volume  of  fine  aggregate  is  determined  by  the  engineer  on  the  basis 
of  py§t  experience  and  the  strength  the  concrete  must  have.   Arbi- 
trarily selected  proportions  seldom  exceed  1:4:8,  which  is  a  lean 


Civil  Engr-8.  Assignment  14.  Page  3. 

mixture  used  only  in  large  masses  for  unimportant  ;vork»   Arbitrary 
proportions  are  less  than  1:1-1/2:3,  which  is  a  rich  mixture  used 
•where  strength  is  a  prime  requirement.  As  indicated  in  the  text 
the  proportion  of  fine  aggregate  is  sometimes  varied  according  to 
the  proportion  of  void  space  in  the  coarse  material.   In  general, 
arbitrary  proportions  are  made  without  regard  for  the  size  and 
grc-.ding  of  the  aggrebates;  the  method  is,  therefore,  not  scientific 
and  yields  satisfactory  results  only  in  the  hands  of  those  exper- 
ienced in  its  use.   In.  most  instances  the  cement  is  not  economically 
used.   Yet  this  method  is  probably  more  widely  employed  than  any 
other  at  the  present  time. 

Proportions  based  on  voids:-   Study  Article  481-  While  this 
method  is  not  in  general  use  it  is  believed,  by  those  who  use  it, 
to  be  quite  scientific.   The  text  points  out  the  inaccuracies  in 
the  method  and  some  of  the  errors  in  the  assumptions  upon  which  the 
method  is  based. 

Proportions  based  on  minimum  yie Id:-   btudy  Article  482. 
The  method  described  in  this  article  is  sometimes  called  "Propor- 
tions based  on  Maximum  Density"  and  "Proportions  by  Trial  Mixtures". 
It  is  a  very  satisfactory  method  and  gives  immediate  results  if 
only  one  fine  and  one  coarse  aggregate  are  available.   It  is  not 
well  adapted  for  the  selection  of  aggregates  when  there  are  several 
of  each  type  available.   When  the  method  is  applicable  it  deals 
with  the  materials  mixed  under  field  conditions  and  yields  good 
results. 


••    •'     '      :. 


.vssignraent  14.  page  4. 

Proportioning  by  mechanical  analysis : -   Study  fs t ic le  433 . 
Tne  methods  of  proportioning,  concrete  aggregates  previously  des- 
cribed might  be  classed  as  cut -and -try  methods.   The  use  of  me- 
chanical cr  sieve  analysis  of  aggregates  gives  the  engineer  an 
opportunity  to  make  intelligent  use  of  the  materials  a^  his  disposal 
anc  brings  proportioning  out  of  the  rule -of -thumb  class  into  the 
scientific  field. 

Mechanical  analysis  was  probably  first  used  to  proportion 
coacrete  aggregates  by  Fuller  and  Thompson  in  1907.   Their  method 
of  proportioning  is  described  in  the  text  in  Article  483.   This 
method  will,  in  general,  give  a  dense,  impermeable  concrete.   It 
permits  the  determination  of  the  best  proportions  of  coarse  and 

fine  aggregates;  it  also  enaoles  the  engineer  to  tell  -what  sizes 

of  material;.- should  be  added  or  tvhat  sizes 
/should  be  screened  out  to  improve  trie  grading  of  given  aggregates. 

By  this  process  he  is  aole  to  o&tain  an  ideally  graded  aggregate 
which,  in  large  work,  may  also  be  found  to  be  economical,  inasmuch 
as  the  cost  of  screening  and  handling  the  aggregates  may  be  less 
than  the  cost  of  the  additional  cement  that  would  be  required  to 
produce  concrete  of  equal  strength  and  imperviousness  from  ungraded 
materials.   The  cement  ratio  is  usually  assumed,  being  taken  as  the 
ratio  of  cement  to  total  aggregate  a&  1:7.   The  ratio  of  cement  to 
sand  and  coarse  aggregate  may  come  out  as  1:  2.3:4.7,  depending 
upon  the  combination  that  most  nearly  approaches  the  ideal  curve. 
The  proportions  may  be  expressed  by  weight  or  volume. 


...        ,.    t.    '.}•*«:•.. 


Civil  Lngr-3.  Assignment  14.  Page  5. 

Fineness  modulus  method  for  proportioning  concret.^:-  Read 
^pp<=ndix  3,  pages  815  to  824  inclusive.  This  information  is  given 
in  mere  detail  by  Duff  A.  Abrams  in  Bulletin  1  of  the  Structural 
I'aterials  Research  Laboratory,  Lev;is  Institute,  Chicago  DESIGN  OF 
CONCRETE  ...JXiURES.  Abrade '  method  of  proportioning  is  based  upon 
the  principle  that  v;ith  given  concrete  materials  the  quantity  of 
mixing  water  used  determines  the  strength  of  the  concrete  so  long 
as  the  concrete  is  plastic  and  the  aggregate  is  not  too  coarse  for 
the  quantity  of  cement  used.   The  relation  between  strength  and  water 
ratio  is  shc-vn  in  Figure  1  on  page  816.  Water  ratio  is  the  usual 
designation  for  the  ratio  of  volume  of  water  to  volume  of  cement  as 
defined  on  page  316.  Figure  1  is  very  important,   it  is  unfortunate 
that  the  same  symbols  should  have  been  used  to  designate  two  differ- 
ent mixes.   If  it  is  remembered,  however,  that  the  concrete  must  be 
plastic,  the  difficulty  will  be  overcome.   Notice,  for  instance,  that 
x  is  used  to  designate  a  1 :2  mix  as  well  as  a  1 ;9  mix.  The  symool, 
however ;  could  not  designate  the  latter  mix  in  the  upper  part  of  tfoe 
curve.   In  this  part,  it  indicates  strengths  of  approximately  6,000 
I'D.  per  sq.  in,  and  since  the  cor  re  spending  water  ratio  is  0.50, 
very  dry  mix  would  result  if  the  proportions  were  1:9.   These  x's 
must,  therefore,  represent  the  1:2  mix.   The  1:9  evidently  is  repre- 
sented by  those  marks  under  1,000  Ib.  per  sq.  in.  and  the  1:2  by 
those  above  that  strength 

The  amount  of  mixing,  water  used  must  be  carefully  considered. 
This  factor  has  not  been  taken  into  account  in  those  methods  of  pro- 
portioning so  far  discussed  in  the  assignment,  Figure  1  indicates 


•;•::    ,'V. 


Civil  Engr-8.  Assignment  14-  page  6. 

the  effect  of  excess  -water.  A  slight  excess  of  water  may  reduce 
the  strength  as  much  as  40%.  Abrams '  tests  show  that  the  strong- 
est concrete  is  that  which  requires  the  least  amount  of  -water  in 
terms  of  cement  (water  ratio;  to  produce  concrete  of  the  required 
consistency,   i/vith  a  given  aggregate  and  increasing  amounts  of 
cement  -  that  is.  increasing  the  richness  of  the  mix-  the  -water  re- 
quired to  produce  a  plastic  consistency  will  give  a  decreased 
Tiater  ratio.  This  is  in  accordance  with  previous  tests  which  show 
that  for  the  same  aggregate  the  richer  mixtures  are  the  strongest. 

While  the  effect  of  water  on  the  strength  of  concrete  had 
been  known  in  a  general  way  Abrams  was  the  first  to  express  the  re- 
lation in  the  definite  terms  of  water  ratio  and  make  tests  covering 
a  wide  range  of  aggregates  and  mixtures.  He  found  that  aggregates 
of  considerable  difference  in  grading  may  give  the  same  strength 
but  that  there  is  a  definite  relation  between  the  grading  of  the 
aggregate  and  the  quantity  of  water  required  to  produce  a  plastic 
concrete.   The  size  and  grading  of  the  aggregate  and  the  proportion 
of  cement  all  affect  the  amount  of  water  necessary  to  produce  a 

workable  concrete.   The  fineness  modulus,  ^vhich  is  defined  on  page 

is 
815  -  see  also  table  1  on  page  8 17, /a  measure  of  the  grading  of  a 

material.   A  coarse  aggregate  may  have  a  fineness  modulus  over  7.00 
while  a  fine  sand  may  be  as  low  as  1.25   The  amount  of  water  is 
required  to  :vet  an  aggregate  of  a  given  fineness  modulus  is  always 
the  same  irrespective  of  its  grading.   Study  the  relation  betwe.-en 
fineness  modulus  and  strength  as  given  in  Figures  2  and  3  on  pages 


Civil  Engr-3.  Assignment  14. 

817  and  818  respectively. 

Read  cart3 fully  the  outline  of  method  of  designing  concrete 
mixes  beginni;Dg  on  page  821.  Add  the  following  to  the  paragraph 
marked  1.  Experience  or  trial  is  the  only  guide  in  determining 
the  relative  consistency  of  concrete  necessary  in  the  work.  A 
relatix^e  consistency  of  1.00  is  dry  and  requires  taaiping.  Con- 
crete having  a  relative  consistency  of  1.10  is  about  the  driest 
that  can  be  used  for  concrete  road  construction.  For  most  rein- 
forced concrete  construction  the  relative  consistency  should  be 
about  1.20;' and  it'  should  never  be  aoove  1.25 

It  is  not  expected  that  you  be  able. to  design  .a  concrete 
mixture  by  Abrams '  method,  but  you  should  be  able  to  tell  in  a  gen- 
eral way  how  it  is  done.  Remember  the  following  criterion:  Use 
the  smallest  quantity  of  mixing  water  that  will  produce  a  concrete 
of  the  required  plasticity. 

Proportioning  by  surface  areas  :-   This  method  of  proportion- 
ing is  not  described  in  the  text.   It  was  proposed  by  L.N.  Edwards, 
who  applied  his  theory  to  the  proportioning  of  mortars.  R.B-  Young 
later  used  the  surface  area  method  to  proportion  concrete  aggregates 
The  underlying  principle  assumes  that  the  strength  and  other  prop- 
erties of  mortars  and  concretes  are  dependent  upon  the  amount  of 
ceirent  used  in  relation  to  the  total  surface  area  of  the  aggregates. 
The  use  of  the  method  is  simplified  by  tables  prepared  by  Edwards 
and  Young  from  which  the  surface  area  of  an  aggregate  can  be  de- 
termined i&hen  its  sieve  analysis  is  known.   They  have  also  made 


'.f 


Civil  Engr-8.  Assignment  L*.  Page  8. 

diagrams  which  give  the  relation  of  strength  to  ratio  of  cement 
to  surface  area.  These  latter  diagrams  have  been  prepared  from 
actual  test  data.  When  several  aggregates  are  available,  the  best 
combination,  -which  is  also  the  most  economical,  is  the  one  which 
has  the  least  surface  area  for  a  given  volume.  The  effect  of  water 
on  the  strength  has  been  taken  into  account  in  this  method  of  pro- 
portioning. When  the  method  is  used  in  the  field,  as  it  has  been, 
very  successfully,  by  R.B.  Young,  the  water  content  and  cement  con- 
tent are  changed  in  the  same  proportion  until  the  desired  consist- 
ency is  obtained-   This  procedure  does  not  effect  the  strength  of 
the  ;nix.   It  is  not  always  necessary  to  change  the  water  ratio 
determined  in  the  laboratory. 

Comparison  of  methods  of  proportioning  concrete:-  The 
methods  of  arbitrarily  selected  proportions,  proportioning  by  voids, 
and  proportioning  by  minimum  yield  do  not  require  a  laboratory 
study  of  the  aggregates,  but  they  may  be  wasteful  of  cement.  When 
high  strength,  imperviousness  and  resistance  to  abrasion  are  required, 
the  proportioning  must  be  done  with  more  care  and  the  methods  based 
upon  sieve  analyses  yield  economical  and  satisfactory  concretes. 
Abrams '  Fineness  Modulus  method  and  the  Surface  Area  Method  are  proo- 
ably  most  satisfactory,  in  such  cases,  since  they  were  determined 
by  t-ests  in  which  a  wide  variety  of  aggregates  was  used.   For  in- 
stance, Fuller  and  Thompson's  method, which  led  to  the  conclusion 
that  concrete  of  maximum  density  was  the  strongest,  was  based  on 
tests  of  a  very  limited  number  of  aggregates.  Abrams'  tests,  in 


Civil  Engr-8  i.ssignr.ient   14.  Page   9. 

the   determination  ana    study   of  the  fineness  modulus  Method,    baseo 
on  a  much  ^;ider   selection  of  concrete  aggregates   proved    on  the 
contrary  that   concrete   of  maximum  density  was  not  always  the 
strongest. 

Proportions  commonly  used    in  different   constructions.—     Read 
Article   454.      Do  net  attempt  to  memorize   the  tabulation  given  in 
this  article.     The    l;2:-i  concrete   is  a  common  standard.     -Sometimes 
a   strength  specification  of  2,000   lo.    per  sq.    in.    at  28  tteys,    is 
made . 

Jesting  the  quality  of  -concrete  :~       Strength  tests  are  most 
valuabl-e   in  determining  the  quality  and  uniformity   oi  concrete.  1'he 
usual  specimen  is  a  6  by  12   inch  cylinder,   tested   at  28  days.     I1  he 
specimens  should  be  poured  with  concrete  ta^en  from  the  mixer   or 
just  before   it   is  placed   in  the   structure.     Rea<3  Article  435. 

Quantities   of  materials  required  for   one  cubic  yard   of 
concrete:-       Read  article  486.      Omit  laoles  4  and   5.     Remember 
Fuller1s  rule   as  given  on  page  434. 

Interpretation  of  the   meaning,   of  proportions:-     Study  Article 
487;    it    is    important,      ihe   statements   given   in  this  article  will  be 
evident  to  the   student  v;no  has   stadieo  the  assignments  up  to  this 
point.      If  two  cuoic   feet   of  sand  are  mixed  with  four  cubic   feet   of 
rock  it   is   obvious  that  the  combination  will  not   fill  a   six  cubic 
foot  measure.     When  the   proportions    of  fine  and   coarse  aggregates 
are   stated,   the   specifications   should   read   "each  of  the  con- 
stituent materials   shall  be  measured    separately". 


Civil  Engr-8.  Assignment   14.  Page   10. 

QUESTIONS 


1.  What  is  meant  by  proportioning  as  applied  to  concrete  aggre- 
gates? 

2.  How  are  the  relative  amounts  of  fine  and  coarse  aggregates 
determined  in  the  method  called  aroitrary  selection? 

3-  What  determines  the  ratio  of  cement  to  total  aggregates  in  the 
method  of  arbitrary  selection? 

4.  What  are  the  errors  in  the  assumptions  used  in  proportioning 
concrete  aggregates  by  voids? 

5.  Discuss  the  adapt ibility  and  limitations  of  the  proportioning 
of  concrete  aggregates  by  trial  mixtures. 

6-  Describe  Fuller  and  Thompson's  method  of  proportioning  con- 
crete. 

7.  What  are  the  advantages  of  methods  using  mechanical  analyses 
over  earlier  methods  in  which  such  analyses  were  not  used? 

6.  Define  water  ratio  as  used  in  Abrams '  method  of  proportioning. 

9.  What  is  meant  by  the  term  fineness  modulus? 

10.  How  does  the  amount  of  mixing  water  used  affect  the  strength 
of  concrete? 

11.  What  is  the  surface  area  method  of  proportioning  concrete? 

12.  Which  of  the  methods  discussed  is  the  most  widely  applicable 
and  why? 

13.  Approximately  how  much  cement,  sand,  and  stone  will  be  requir- 
ed to  make  20  cubic  feet  of  concrete  if  the  proportions  are 
1:2:4? 


OF  CALIFOHN  la  LXj^Nb'ION  DIVISION 
Correspondence  Courses 

iv.aterials  of  Engineering  Construction 
Civil  Engr.-3  Assignment     15  Prof.   C.   T. 

klXING,   JrUC  ING  AND  CURING  OF  CONC&ETE. 

Principles   of  proper  mixing.-     Study  Article  488.      The 
materials  should  be  uniformly  distributed  throughout  the  mass   so 
that  the  mixture   is  hor.o?ene->us  and  uniform  in  color.     The   same 
amount   of  v,ater   should   be  added  to  each  batch  in  order  to  maintain 
the  desired  consistency. 

In  hand  nixing  the  water   is  usually  measured   in  buckets 
v:hile  machine  mixers  are  provided  v/ith  -water -measuring  devices. 

Kand  mix ing. -     Read     article  489.      The  following 
specifications  were  taken  from  the   latest  reports   of  the  A«S«T«L. : 
"i.hen  hand  mixing  is  authorized   oy  the  engineer   it  shall  be  done  on 
a  water-tight  platform.     The   sand  shall  be  spread   on  the  platform 
and  the  cement   spread   evenly  over  the   sand.      The  material  shall  then 
be   shoveled   into  a  cone   shaped  pile  by  casting  centrally   on  the 
pile.     This  pile   shall  then  be  divided  by  casting  into  two  or  more 
cone   shaped  piles  and  the   operation  of  dividing  and   reuniting 

continued  until  the  batch   is  uniform  in  color.      Only   sufficient 
water  to  produce  the  desired  consistency  shall  then  be  added  by 

sprinkling  as  the  batch   is  turned.      The  coarse  aggregate  previously 
moistened  shall  then  be  mixed  v/ith  the  mortar   in  the  manner 
specified  for  mixing  sand   and  cement."     This  method   is  productive     of 
better  results  than  can  be   secured  by  the  methods  commonly  used. 


£ngr.-8  Materials  of  Engineering  Construction.  Assn. 15,  pgge  2 

Machine  mixing.-  Study  Article  490.   The  A.  S.T.k.  specifica- 
tions read,  "Li:: ing,  unless  otherwise  authorized -by  the  engineer, 

shall  be  done  in  a  batch  mixer  of  approved  type "  The  Continuous 

mixer,  while  it  can  be  operated  rapidly  and  cheaply,  rarely  gives 
a  uniform  product.   Since  it  cannot  be  relied  upon,  the  batch  mixer 
is  preferable. 

The  tirje  of  mixing  is  specified  as  follows:  "The  mixing  of 
each  batch  shall  continue  not  less  than  1  minute  after  all  the  materials 
are  in  the  mixer,  during  which  time  the  mixer  shall  rotate  at  a 
peripheral  speed  ef  about  200  feet  per  minute....."  Although  the 
data  given  in  the  text,  shown  in  Figures  9  and  10,  would  indicate  that 
a  longer  period  of  mixing  vould  be  desirable,  and  the  A. S«£«k«  formerly 
recommended  1  1/2  minutes  as  the  mixing  tL.,e,  recent  tests  seem  to 
•warrant  the  minute  mix. 

fixing  produces  a  change  in  the  consistency  of  concrete,  the 
water  content  remaining  constant.   The  change  is  particularly 
marked  between  30  seconds  and  1  minute,  but  the  additional  change 
after  1  minute  is  slight. 

It  is  possible  to  obtain  the  same  degree  of  plasticity  (consistency) 
oy  mixing  for  1  minute  as  -would  be  obtained  oy  mixing  for  1/2  minute 
with  25f0  more  water.  Contractors  sometimes  resort  to  the  shorter 
mixing  periods  in  order  to  save  time,  and  add  more  water  in  order  to 
bring  the  concrete  to  the  desired  consistency.   The  A.  S.T.M« 
specifications,  however,  do  not  permit  the  retempering  of  mortar  or 
concrete,  that  is  the  remixing  with  or  without  additional  cement, 
aggregate,  or  water. 


Engr.-8,  materials  of  Engineering  Construction.  Assn.  15,  page  3 
Hand  vs.  machine  mixing*-  Head  Article  491.  Good  mixing 

can  be  secured  by  hand  as  well  as  machine  mixing;'  the  former 
however,  requires  heavy  labor  and  is  usually  not  thoroughly  done. 
For  all  except  the  smallest  jobs,  machine  mixing  will  be  less 
expensive  than  hand  mixing. 

The  tests  referred  to  in  this  article  would  indicate  that 
hand  mixing  is  inferior  to  machine  mixing.  With  reference  to  hand 
mixing  as  it  is  usually  done  ,  this  is  probably  true.  The  last 
sentence  in  the  article,  which  states  that  the  hand  mixed  concrete 
referred  to  in  the  test  required  more  water  to  bring  it  to  the  con- 
sistency of  that  mixed  by  the  machine,  shows  that  the  mixing  by 
hand  had  been  slighted.   If  the  hand  mixing  had  been  thoroughly 
done  there  would  have  been  no  marked  difference  between  the  concrete 
produced  by  the  two  methods. 

Handling  of  concrete.-  Read  Article  4S2.   The  fundamental 

no 

principle  in  the  handling  of  concrete  is  that  there  must  be/ oppor- 
tunity afforded  for  a  segregation  oetween  the  mortar  and  the 
course  aggregate. 

Besides  the  methods  descrioed  in  the  text,  concrete  is 
transported  in  large  motor-trucks  from  a  central  mixing  plant 
in  road  construction.   Sometimes  the  hauls  are  very  long.   In  order 
to  determine  the  effect  of  such  transportation  the  Bureau  of  Public 
Roads  has  recently  made  a  series  of  tests  in  which  the  concrete  was 
hauled  for  diffenent  periods,  up  to  3  hours.   They  found  that  after 
45  minutes  of  hauling  the  concrete  became  too  stiff  for  hand  finishing, 
but  that  the  strength  was  not  reduced  as  long  as  the  concrete  remained 
workable. 


s  *f  iMgiueer ing  Construction.   ..ss.  .  '.E, 
Concrete  should  not  be  deposited  under  water  if  it  is 
practical  to  exclude  the  water  by  means  of  cofferdams.  There  is 
always  uncertainty  in  depositing  concrete  under  water  even  if  the 
methods  described  in  the  text  are  used*  If  it  is  impractical  to 
use  other  methods  concrete  should  be  placed  under  water  only  under 
experienced  supervision.  This  is  particularly  true  in  the  case  of 
sea  water.  The  usual  methods  in  which  the  trernie,  drop-bottom 
bucket s,  and  bags  are  used,  are  described  in  the  text. 

Placement  of  concrete.-  Read  Article  493.  Concrete  should 
be  placed  in  the  forms  in  its  final  position  so  as  to  make  re- 
handling  unnecessary.  It  should  be  placed  in  uniform  horizontal 
layers  and  not  allowed  to  flow  down  a  slope  so  as  to  permit  a 
segregation  of  fine  and  coarce  materials.  During  and  immediately 
after  depositing,  the  concrete  should  be  thoroughly  compacted  by 
spading  or  rodding.  Some  compacting  is  necessary  to  make  the 
concrete  flow  into  the  corners  of  the  molds  and  around  the  rein- 
forcement since  it  is  usually  mixed  with  as  little  water  as  possible. 
The  days  of  wet,  soupy  concrete  which  did  not  require  rodding  are 
over.  Relatively  dry  concrete  can  be  used  in  the  construction  of 
concrete  pavements  since  power -driven  tampers  and  metal  rollers  can 
be  used  to  compact  it.   Concrete  used  in  reinforced  construction 

must  be  more  plastic  so  that  it  can  be  properly  placed. 
d^*v  be. 

Cement  mortar  *«  deposited  by  an  apparatus  known  as  a  cement 
^ 

gun.  This  device  is  described  on  page  444  of  the  text.  The  cement 
gun  is  being  widely  used.   It  produces  a  dense   strong  mortar. 


Engr.-S    Materials  of  Engineering  Construction,   .-.ssn.    15,  page   5. 

Joining  old  and  new  work.-     Read  Article  494.      If  work  is 
not  continuous,   joints  cannot  be  avoided.     In  making  joints  every 
precaution   should  be  taken  to  make  the  bond  as  strong  as  possible. 
The  methods  of  bonding  are  described  in  this  article.     Laitance 
is  mentioned.     It  is  a  whitish   scum  which  comes  to  the    surface  of 
wet  concrete.      Laitance  is  formed  when  concrete  is  deposited  under 
water  or  vrhen  water  comes  to  the   surface  of  the  concrete  xvhich  has 
been  mixed  with  an  excess  of  water.     It  is  composed  of  finest 
particles  of  cement  and  the  dirt  in  the  aggregates.     While  the 
composition  of  laitance   is  practically  the   same  as  that  of  cement  it 
does  not  have  the    same  properties.      It  does  not  harden  or  acquire 
much  strength  and  consequently  if  it  is  not  removed  it  prevents  tfoe 
bonding  of   successive  layers  of  concrete. 

Forms. *»     Read  Article  495.     Forms  should  be    sufficiently 
tight  to  prevent  the  leakage  of  mortar  and  they   should  be   so 
braced  andtied  together  as  to  maintain  their  position  and   shape. 

Before  concrete  is  deposited  in  the  forms  all  debris  should 
be  removed  from  the  place  to  be  occupied  by  the  concrete.     The 
forms  should  be  cleaned  fcnd  thoroughly  wetted  or  oiled  to  prevent 
absorption  of  water  from  the  concrete.      Steel  has  been  used  for 
some  time  for  forms  for    concrete  pipe,   tunnels,    sewers,   curbs,   retain- 
ing walls  and  dams,   and  it   is  gradually  replacing  wood  for    formwork 
ir.   standardized  building  construction. 

Read  the   information  regarding  the  pressure  of  wet  concrete 
againit'.the  forma  .as  given  on  page  447.       More  recent  experiments 
give   lovrer  values.     The  most  reliable  are  given  in  POURING  AND 


Engr.-8  Materials  6f  Engineering  Construction.  Assn.15,  page  6. 
PRESSURE  TESTS  OF  CONCRETE  by  Slater  and  Goldbeck,  U.S. Bureau  of 
Standards,  Technologic  Paper  No.  175.  Their  principal  conclusions 
are:  (a)  The  maximum  pressure  against  the  forms  during  pouring  of 
concrete  izras  fouAd  to  be  equivalent  to  that  of  a  liquid  weighing 
about  124  Ib.  per  cu.  ft.  (b)  The  maximum  pressure  was  found  to  be 
that  due  to  the  head  of  concrete  existing  at  the  end  of  about  40 
minutes.  After  that  time  the  pressure  gradually  decreased  in  spite 
of  increasing  the  head  of  concrete.  These  data  are  of  value  in 
the  design  of  forms. 

The  time  for  removing  forms  is  determined  by  the  strength  of 
the  concrete.  As  indicated  in  this  article  the  strength  of  the 
concrete  can  be  found  only  by  actual  tests.  The  removal  of  the 
forms  from  concrete  structures  that  have  not  developed  sufficient 
strength  has  resulted  in  many  failures.  On  the  othsr  hand,  much 
money  value  is  sacrificed  if  the  forms  are  left  on  too  long.  Weather, 
position  of  the  form,  quality  of  the  cement,  and  the  load  are  the 
principal  factors  which  influence  the  time  of  removal  of  the  forms. 
Warm,  dry  weather  hastens  the  setting  and  hardening  of  concrete, 
while  cold,  damp  weather  retards  hardening,  Forms  for  horizontal 
members,  such  as  beams,  should  remain  in  place  longer  than  forms 
for  vertical  members,  such  as  columns  and  walls.  The  forms  may 
obviously  be  removed  sooner  from  concrete  made  with  quick-hardening 
cement  than  from  normal  concrete.  When  the  load  carried  by  a 

KA 

member  i<5  nearly  all  live  load/ such  as  machinery,  equipment,  and 
people,  the  forms  may  be  removed  sooner  than  when  the  total  load 
on  the  member  is  largely  dead  load.  For  this  reason  roof  forms  and 


Engr.-8  Materials  of  Engineering  Construction .  ^ssn.  15,  page  7. 
top -story  columns  arc  left  on  longer  than  those  for  other  floors. 
The  following  table  is  abstracted  from  Hool  and  John  son ' s  CONCRETE 
ENGINEER'S  HANDBOOK: 

Removal  of  forms 


Above  60°  p. 

50-60°  F. 

40-50°  F. 

Column   Sides 
Beam  Bottoms 

Within  3  days 
Within   14  days 

5  days 
18  days 

10  days  or  more 
24  days  or  more 

Expansion  joints*-  Read  Article  496.  Concrete  shrinks 
when  it  sets  in  air  and  expands  when  it  sets  in  water.  After  it 
has  set,  changes  in  moisture  content  cause  volume  changes.  Concrete 
expands  when  it  is  wet  and  contracts  when  it  dries  out.  Expansion 
and  contraction  are  also  caused  by  heating  and  cooling  respectively. 
The  forces  which  produce  volume  changes  may  counteract  one  another 
so  that  there  will  be  no  effect  on  the  concrete.  They  may  also 
act  together  or  separately  and  cause  volume  changes  which  become 
evident  as  expansion  and  contraction. The  change  in  length  in 
100  ft.  of  concrete  is  about  O.Sinches  per  100  degrees  Fahrenheit. 
In  contraction,  this  produces  cracks  in  walls,  walks  and  pavements. 
In  expansion,  it  buckles  curbs  and  walks  unless  expansion  joints 
are  provided.   Long  stretches  of  wall  may  be  built  without  expansion 
joints  provided  that  enough  steel  is  put  in  to  hold  the  concrete 
together-  The  steel  does  not  stop  the  movement  but  it  distributes 
the  total  change  in  length  and  produces  a  large  number  of  very  fine 
cracks  \?hich  do  no  damage.  The  A.S.T.M.  specifications  provide 
that  "structures  exceeding  200  ft.  in  length  andof  width  less  than 


2ngr.-S     ..later Lils  of  Engineering   Construction.   Assn  15,  page  &• 
about  one-half  the   length,    shall  be  divided  by  means  of  expansion 

joints,    located  near  the  middle,   but  not  more  than  200  ft*   apart > 
to  minimize  the  destructive  effects  of  temperature  changes  and 
shrinkage.*..."     When   such  expansion  joints  are  used  they   should 
be  arranged  to   separate  completely  the  parts  of  the  building  and 
should  extend  from  the  bottom  60  the  top  of  the   structure.     An 
expansion  joint   should   separate  all  parts  such  as  beams,   columns 
and   slabs  from  the  main  part  of  the   structure.     When  expansion  joints 
are  placed  in  retaining  walls  they   should  be   spaced  about  30  ft. 
apart. 

Curing.-       Read  Article  497.     The  process  of  keeping  concrete 
damp  is  called  curing.      Concrete   is  cured  by  immersion,    sprinkling 
and  the  use  of   steam.     Hydration  of  the  cement  goes  on  after  the 
concrete  has  hardened,    so  that  it   is  necessary  to  prevent   it  from 
drying  out  too  rapidly.     Allowing  the  forms  to  remain  in  place  helps 
to  retain  the  moisture.     Newly  laid  concrete  pavements  are  protected 
from  the  direct  rays  of  the   sun  by  means  of  canvas  and  after  the 
concrete  has   set,   it  is  covered  with  moist  earth  or  flooded  vdth 
water . 

Concrete  products  such  as  described  in  Chapter  XV  are     cured 
by  the  three  methods  mentioned  above,   immersion,    sprinkling  and  the 
use  of   steam.     The  American   Concrete   Institute   specifies  protection 
from  the   sun  and strong  currents  of  air  for   at   least  7  days; 
continuous  sprinkling  andmaintenance  of  a  temperature  of  not   less 
than  50  degrees  Fahrenheit  and   storing  in     the  yards  for   about  £1 
days  before   shipment.     For   steam   curing,   their   specifications 


Engr.»3  ^at-arials  of  Engineering  Construction.  Assn.  15,  page  9t 
read,  "The  products  shall  be  removed  from  the  molds  when  the 

conditions  permit  and  shall  be  placed  in  a  steam  curing  chamber 
containing  an  atmosphere  of  steam  saturated  with  water  for  a 
period  of  at  least  48  hours.  The  curing  chamber  shall  be  kept  at 
a  temperature  between  100  and  130  degrees  Fahrenheit-  The  product 
shall  be  removed  and  stored  for  at  least  8  days." 

Protection  against  freezing.  -  Read  Article  498.  Concrete 
should  not  be  mixed  or  deposited  at  a  freezing  temperature  unless 
precautions  are  taken  to  overcome  the  effects  of  low  temperature. 
Uork  nay  be  carried  out  during  freezing  weather  by  heating  the 
materials  and  the  structure  or  by  the  addition  of  some  substance  to 
lower  the  freezing-point  of  water.  Wherever  the  temperature  drops 
to  35  to  40  degrees  Fahrenheit  the  materials  should  be  heated. 
After  concrete  has  been  placed  it  should  be  protected  against  the 
cold  for  48  hours  to  5  days,  dependingupon  the  temperature.  ?Jhen 
important  structures  must  be  constructed  during  periods  of  low 
temperature  they  are  completely  enclosed  with  tarpaulin  or  heavy 
canvas  even  though  they  may  be  large  buildings.  The  interiors  are 
then  heated,  as  explained  in  the  text. 


QUESTIONS 

1.  7/hat  constitutes  proper  mixing? 

2.  Describe  the  method  of  hand  mixing  recomnended  by  the  A-  S-T.M 

3.  ^/hat  are  the  principal  factors  that  should  be  considered  in 
the  purchase  of  a  concrete  mixer? 


Engr.-8     Materials  of  Engineering  Construction-     Assn.   15, page     10 

QUESTIONS,    con. 

4.  How  long   should  concrete  be  mixed  when  a  batch  mixer  is  used? 

5«     What  is  the  fundamental  principle  in  the  transportation  and 
deposition  of  concrete? 

6.  What  methods  are  used  to   deposit  concrete  under  water? 

7.  What  precautions  should  betaken  in  bonding  to  old  concrete  work? 

5.  ?i/hat  approximate   lateral  pressure  is  exerted  against  the  forms 
by  fresh  concrete? 

9.     What  causes  concrete  to   shrink?  What  is  the  effect  of  shrinkage 
and  hovr  is  it  overcome? 

10.     What  precautions  must  be  taken  -when  concreting  at  or  belovr 
freezing  temperatures? 

11*     What  is  meant  by  curing  concrete? 

12.     Why  is  a  batch  mixer  considered  better  than  a  continuous  mixer? 

IS.     In  "what  way  may  the  quality  of  concrete  be  impaired  by  methods 
of  placing  in  ordinary  construction? 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 
Correspondence  Courses 

Materials  of  Engineering   Construction 

Civil  Engr.-8  Assignment   16.  Professor   C.T.Wiskocil 

PHYSICAL  PROPERTIES  OF  MORTAR  AND  CONCRETE. 

Introduction.-     Read  Article  499.     While  the  effect  of  the 
important  factors  which  influence  the  physical  properties  of  mortar 
and  concrete  are  discussed  in  this  assignment  it   should  be  remembered 
that  in  any  investigation  all  factors  are  not  known,  and  that  it 
is  consequently  not  possible  to  control  them  all  properly,   and  that 
the  re  suits, therefore,    should  be  taken  as  being  indicative  only. 
In  many  of  the  data  given  in  the  tejtfc,  no  attempt  is  made  to  state 
the  conditions  under  which  the  tests  were  made.     This  information 
is  frequently  omitted  even  from  the  original  publications  fron 
which  the  data  were  compiled. 

Strength  of  mortar s» -     Read  Articles  500  to  506  inclusive. 
The  principal  use  for  mortar  is  in  the  construction  of  masonry.  Mien 
strength  is  required  in   stone,  brick  or  terra  cotta  structures, 
Portland  cement  mortar  is  used.     Cement  mortars  in  various  proportions 
are  also  used  for    stucco.      Stucco  may  be  defined  as  a  material  used 
in  a  plastic    state  to  form  a  hard  coating  for  the  exterior  walls 
or  other   surfaces  of  any  building  or   structure.     Mortar  is  relatively 
unimportant  when  compared  to  concrete « 

The  effect  of  proportion  of  cenent  on  the   strength  of  mortars 
is  discussed  in  Article  $00  and   shown  in  Figure   1  on  page  452. 
Compare  the   strength  of  neat  cement  given  in  Figure   14  on  page  332 


Engr.-8     Materials  of  Engineering  Construction       Assn.    16.  page  2. 

• 
with  the  compressive    strength  given  for  neat  cement  on  page  452. 

Compare  also  the  figure  on  page  354  with  that  on  page  452.  The 
strength  of  neat  cement  as  well  as  mixtures  of  cement  and  fine 
aggregate  varies  with  the  brand  of  cement  used  -  cements  cb    not 
all  have  the   same  cementing  value.   Other  factors  which  affect  the 
strength  of  cement  and  cement  mixtures  are:     the  amount  of  water 

used  in  mixing,  the  conditions  of   storage  and  testing  and  the 

453 
gradation  of  the   sand  (as  shown  in  the  figures  on  pages  452/and  454.) 

Because  of  the  relative  unimportance  of  mortar  as  a  structural 
material  make  no  attempt  to  remember  the  data  in  Article  500  to  502 
inclusive. 

Probably     the  most  comprehensive  tests  of  ceuent  mortars  are 
reported  in  Technologic  Paper  No.   58  of  the  U. S.Bureau  of   Standards. 
From  this  publication  the  following  information  is  taken  u(a)  The 
quality  of  a   sand  cannot  be  judged  from  its  gradation  alone. (b)  For 
most  fine  aggregates  the  highest    strengths  are  obtained  with  those 
having  a  gradation  of  particles  approaching  a   straight  line,  but 
often  materials  having  a  gradation  varying  widely  from  a   straight 
line  will  give  high   strength  in  mortars*    (c)No  fine  aggregate 
should  be  rejected  because  of  its  silt  content   (determined  by 
washing  or  assuming  the  material  passing  the  No.   200    sieve  as  silt) 
as  it  may  be  advantageous  even  in  relatively  large  quantities  or 
detrimental  in  small  quantities,   depending  upon  its  form,   character 
and  distributicn.(d)The  only   satisfactory  method  of  determining  the 


Engr.-8     Materials  of  Engineering  Construction.     As.sn.    16,  page  3. 

value  of  a  fine  aggregate  in  mortar  mixtures  is  to  test  it  in 
the  mixture,   in  the  proportion  to  be  used,   exposed  to  the    same 
conditions  as  in  the  proposed   structure."     These  above  remarks 
are  of  importance  in  the  consideration  of  mortar. 

The   strength  in  compression  and  in  cross  bending  can  be 
estimated  with   sufficient  accuracy  from  the  average    strength 
of  neat  mortar,   10,000  lb.  per   sq.   in.    (compression)  and  1,000  lb. 
per   sq.   in. (cross  bending),   and  from  the  general   shape  of  the  curves 
on  page  452,  which  give  the  relation  between   strength  and  proportion 
of  cement  to   aggregate.  A  1:6  mortar  has  an  approximate     compressive 
strength  of  1,000  lb«  per   sQ.   in.  and  an  average  transverse    strength 
of  300  lb-  per   s£.   in. 

The  effect  of  the  amount  of  mixing  water  on  the   compressive 
strength  of  mortars  is   similar  to  that   shown  on  page  816  in 
the  case  of  concrete.     This  relation  for  neat  and  1:5  mortars  is 
shown  in  Figure  10  on  page  33,  Bulletin  No.   8,   of  Structural  Materials 
Research  Laboratory,   Lewis  Institute,    Chicago. 

Mica  decreases  the  compressive    strength  of  mortar.     Recent 
experiments  made  by  Professor  Abroms  at  Lewis  Institute  bear  out 
this  statement  but  his  tests  indicate  that  the  decrease  is  not  as 
marked  as  that  found  by  Wills.     See  Article  504. 

Tests  reported  in  Bulletin  No.   8  of  the   Structural  Materials 
Research  Laboratory,  previously  referred  to,   indicate  that  the  use 
of  hydrated  lime  decreases  the    strength  of  cement  mortar.     About 


Engr.   8,     Materials  of  Engineering  Construction.     Assn.   16,  page  4. 

8,000  tests  on  briquettes  and  2  by  4  inch  cylinders  were  made  during 
this  investigation*     The  tests  mentioned  in  Article  505,    since  they 
are  few  in  number,   cannot  be  given  as  much  consideration. 

Merely  read  Article  506  on  adhesion  of  mortars;   it   is  relatively 
unimportant. 

Strength  of  concrete.-       Read    Articles  507  to  517  inclusive. 
The    strength  of  concrete   is  affected  by  various  factors,  the  most 
important  of  which  are;   age,  proportions  of  cement  to  aggregate, 
kind  of  aggregate,  amount  of  mixing  water,  and  curing  conditions. 
In  view  of  these  variables,   good  average  figures  to  remember   are: 
2,000  Ib.  per    sq.   in.   in  compression,   200  lb»  per    sq.   in«   in  tension 
and  1,000  Ib*  per   sq*   in.   in  shear  at  28  days.     At  the  age  of  one 
year  concrete  is  about  2  1/2  times   stronger  than  at  28  days,  the 
usual  testing  period.     Concrete  is  a  brittle  material,   and  as  the 
average  values  given  indicate,    is  strongest  in  compression.     Its 
tensile    strength  is  lov;  and  is  neglected  in  the  design  of  reinforced 
concrete   structures.     The   shearing  strength  of  concrete  is  about  1/2 
its  compressive   strength. 

The  compressive   strength  increases  vrith  the  richness  of  the 
mix.     The  tables  on  pages  459,  460  and  461   shew  this  fact  -  but  not 
in  a  form  that  can  be  easily  remembered.     The  following  diagram 
gives  average  values  for   soft  limestone   concrete    stored  in  a  damp 
location*     The  proportions  are  the  total  of  fine  and  coarse  aggregates 
measured   separately.     The  diagram  also  indicates  the  normal  increase 


Engr-8.     Materials  pf  Engineering  Construction.     Assn.    16,  page  5» 

in   strength  with  age.     The  dotted  curve  vas  plotted  from  data  for 
gravel,   hard  limestone  or  hard   sandstone  concrete  28  days  old,  taken 
from  the  report  of  the  Joint  Committee  on  Concrete  and  Reinforced 
Concrete.     The  values  are  based  on  tests  of  8  by  16  inch  cylindrical 
specimens   stored  under   laboratory   conditions* 


5000 


4000 


3000 


2000 


1000 


4 


10      11       12 


Proportion  of  Aggregate  to  one  part  of  Cement 


Figure   1 


Engr.-8       Materials  of  Engineering  Construction*       A.ssn.16,   page  6. 

Under  ordinary  conditions  concrete  will  not   gain  much   strength 
after   one  year  but   if  concrete  does  not   dry  out  its  compressive 
strength  increases  indefinitely.     See  EFFECT  OF  AGE  ON  THE  STRENGTH 
OF  CONCRETE  by  D.   Abrams,  A.    S.  T.M.  Proceedings,   1918,   page  317. 
The  age- strength  relation  for  mortar  and  concrete  is  expressed  by 
the  equation 
og  a  +  k  where   3  is   the  compressive   strength,   a_  is   the  age   and  n  and  £ 

are  constants  whose  value  depends  upon  the  cement  and  other  test 
conditions.     This  equation  has  been  derived  from  tests  in  American 
and  European  laboratories  on  specimens  up  to  nine  years  in  age. 

Since  there  are  so  many  factors  which  affect  the  density- 
strength  relation  (see  Article  509),  density  is  not  a  reliable 
criterion  of  strength. 

The  effect  of   size  of  coarse  aggregate,  v/hich  is  discussed  in 
article  510,    is  well   illustrated  in  Figure  3  on  page  818. 

The  effect  of  proportion  of  mixing  water  on  the   strength  of 
concrete   is  explained  in  Article  511.     The  water  ratio  -   strength 
relation  -  is   shown  in  a  clear-cut,   definite  manner   in  Figure   1  on 
page   816.     The  following  conclusion  is  made  by  Abrams:  Vi/ith  given 
concrete  materials  and  conditions  of  test  the  quantity  of  mixing 
water  used  determines  the    strength  of  the  concrete,    so  long  as  the 
mix  is  of  a  workable  plasticity. 

The  information  in  Article  512   is  relatively  unimportant. 
Remember  that  the  tensile    strength  of  concrete  is  about  1/10  of  its 
compressive    strength. 


Engr.-8     Materials  of  Engineering  Construction.     Assn.   16,  page  7. 

Because  of  its  low  tensile    strength  concrete  without    steel 
reinforcement  is  rarely  used  where  it  would  be   subjected  to  trans- 
verse  loads.     The  discussion  on  transverse    strength  in  Article  513, 
therefore,   is  of  little     importance. 

Read  carefully  the  first  paragraph  of  Article  514.     The 
remainder  of  the  article   is  not  important.     Remember  that  the 
shearing  strength  (punching  shear)  of  concrete  is  about  1/2  of  its 
compressive    strength* 

The  effect  of  type  of  aggregate  is    well  illustrated  in  the 
Joint   Committe  Report    (previously  referred  to)  from  which  the 
following  data  were  taken: 

Granite,  trap  rock  2,200 

Gravel,   hard   sandstone,  hard  limestone  2,000 

Soft  limestone,    soft   sandstone  1,500 

Cinders  ,        600 

fe     &  ^1*  S<7,  I*. 

The  values  given  are  for  compressive    strength^at  28days  for  1:6 
concrete,  the  fine  and  coarse  aggregates  being  measured    separately. 

The  conditions  under  which  concrete  is  cured  have  a  great 
influence  upon  its   strength.     The  following   statements  were  taken 
from  EFFECT   OF   CURING  CONDITION  ON  THE  v/EtoR  AND  STRENGTH  <DF  CONCRETE, 
by  D.A.Abrams,   Bulletin  No.   2,   Structural  Materials  Research 
Laboratory,    Lev/is  Institute,   Chicago.    "All  consistencies  of  concrete 
show  great  increases  in   strength  under  favorable  curing  conditions 
as  compared  with   specimen's  which  were  allowed  to  dry  out  at  once. 

V 

The  dryer  mixes  show  a  more  rapid  improvement  due  to  storage  in  a 
damp  place  during  the  first  few  days  than  the  7/etter  ones.  Even 


Engr.-8     Materials  of  Engineering  Con srbr action.     Assn.   16, page  8. 

» 

three  days  in  damp  sand  results  in  increase  in  strength  of  dryer 

concretes  of  about  35%  as  compared  with  that  of  the  specimen^  stored 
in  open  air  for  the  entire  period.  Concrete  stored  in  damp  sand 
and  tested  danp  is  about  3  times  as  strong  as  similar  concrete 
which  had  been  exposed  to  room  atmosphere  for  the  same  period- 
Protecting  concrete  from  drying  out  for  only  10  days  gives  an 
increase  in  strength  of  about  75%  for  the  dryer  mixes." 

Elastic  properties  of  concrete.**  Read  carefully  Article 
518.   In  it  the  true  elastic  stress-deformation  and  gross 
deformation  curves  are  described-  The  gross  deformation  is  usually 
plotted  against  stress,  as  indicated  in  Figures  12  and  13,  on  pages 
476  and  477  respectively.  These  curves  SHOT;  a  decided  curvature, 
concave  downward,  as  stress-def  or  nation  curves  for  other  brittle 
materials  do;  see  Figure  11  on  page  710.  The  elastic  stress-deform- 
ation relation  is  of  importance  in  the  determination  of  stresses  in 
structural  members  under  load.  Under  long  time  loads,  concrete 
undergoes  a  greater  deformation  than  it  does  for  the  same  load  ap- 
plied for  a  short  period,  as  in  the  usual  testing  machine.  The 
gross  deformation  of  a  given  fiber  cannot  be  used  to  compute  the 
actual  stress;  the  elastic  deformation  must  be  used. 

It  should  be  noted  at  this  time,  that  there  are  investigators 
who  believe  that  the  stress  deformation  curve  for  concrete  up  to  and 
even  over  -.-or king  stresses  is  a  straight  line.  They  show  data  to 
support  their  views  and  state  that  in  their  judgment  the  curvature 
in  most  stress-deformation  curves  is  due  to  inaccurate  apparatus 


Engr«-8     Materials  of  Engineering  Construction,  Assn.   16,  page  9, 

and  technique  on  the  part  of  the   investigator.     Note  that  the    stress- 
deformation  curves  given  in  Figure   12  on  page  476  are  practically 
straight  lines  up  to  1,000  lb.  per    sq.   in.,  which  is  well  above 
working   stresses  for  concrete.     Stress-deformation  diagrams  for  tests 
reported  by  C.T.Wiskocil  in  the  Report  on  California  Highways  - 
California  Automobile   Clubs,    1921,   part   IV,  page   18,   for  concrete 
whose  average  compressive    strength  at  28  days  was  2,430  Ib.   per    sq. 
in.,  were    straight  lines  up  to  an  average    stress  of  1,080  Ib.   per 
sq.    in.      For  2,000  lb.   concrete  the  wor Icing  stresses  vary  from  450 
to  650   Ib.   per    sq.   in.   depending  upon  the   kind  of   stress,  that   is 
whether   it   is  direot  compression  or  extreme  fiber    stress  in  bending. 

Read  Article  519.  The  difference  between  the  initial  and 
secant  moduli  is  explained  and  illustrated.  Since  these  terms 
are  in  use,  their  meaning  should  be  known  by  the  student. 

Read  Article  520.     The  modulus  of  elasticity  of  concrete 
varies  from  about  1,000,000  to  4,000,000  Ib.  per   sq.   in.  For 
2,000  Ib.   concrete  the  average  value   is  about  2,000,000  Ib.   per 
sq.   in.,   being  1/15  that  of   steel.     This  value   is  used  in  most 
design  calculations. 

Poisson's  ratio,   given  in  Article   521,   is  of  value   in 
theoretical  discussions  and  in  the  determination  of    stresses  in 
certain  types  of    structures,    such  as  arch-dams.     For  practical 
purposes  the  ratio  may  be  taken  as  1/10. 

A  change   in  moisture   content,    as  well  as  variation  in  direct 
load  and  change   in  temperature,  has  an  important  effect  on  the 


Sngr.-8  Materials  of  Engineering  Construction.  Assn»  16,  page  10. 

deformations  produced  in  concrete.  Read  carefully  the  first  paragraph 
in  Article  522.   Since  concrete  and  steel  have  practically  the  same 
coefficient  of  expansion  they  change  length  at  the  same  rate,  and 
variations  in  temperature  do  not  cause  any  stress  unless  the  member 
is  restrained.   Changes  in  moisture  content,  on  the  other  hand, 
effect  only  the  concrete,  which  expands  when  it  absorbs  water  and 
contracts  when  it  dries.  After  concrete  sets  it  ordinarily  shrinks 
a  considerable  amount.  This  shrinkage  during  hardening  may  be  as 
much  as  0.05%  in  an  ordinary  structure.   Contraction  in  concrete 
when  it  is  restrained  by  an  external  force,  as  by  other  members 
in  a  structure  or  by  steel  reinforcement,  causes  stress  in  the 
concrete.   In  reinforced  concrete  the  shrinkage  produces  stress 
in  the  steel,  when  the  reinforcement  is  less  than  1.5%  ,  which  may 
reach  ordinary  working  stresses  (16,000  Ib.  per  sq.  in»)   If  the 
amount  of  steel  reinforcement  is  greater  than  1.5^  the  stress 
produced  by  the  drying  out  of  the  concrete  may  reach  the  ultimate 
tensile  strength  of  the  concrete*  The  greater  the  amount  of  steel, 
the  greater  will  be  the  tensile  stress  produced  in  the  concrete  for 
a  given  reduction  in  moisture  content.  Under  atmospheric  conditions 
where  concrete  is  alternately  wet  and  dry  the  alternation  in 

stress  may  crack  the  concrete  even  if  the  stress  is  below  the 
ultimate  tensile  strength  of  the  concrete  as  determined  in  the  usual 

static  test.  Excessive  expansion  and  contraction  can  be  reduced  by 
waterproofing  the  concrete* 


Engr.-8     Materials  of  Engineering  Construction*   Assn.   16,   page   11. 

QUESTIONS 

1.  IVhat   is  the  principal  use  for  cement  mortars? 

2,  Give  the  average  compressive    strength  of  neat  and   1:6  cement 
mortar  when  about   1/2  year   old. 

5*       what   is  the  approximate    strength  of   1:6  concrete    (the  fine  and 
coarse  aggregates  being  measured   separately)   in  compression, 
tension,  and   shear  at  28  days? 

4«       What  would  be  the   approximate   compressive    strength  of  the 
concrete   specified  in  question  3  at  the   age   of  one  year' 

5.  How  does  the  rate   of  increase   in   strength  vary  for   different 
ages?     \Vhat   influences  the   increase   in   strength  besides  age? 

6.  Approximately  what  difference   in  compire  ssive    strength  would 
you  expect  between  (a)   concrete  exposed  to  air  and   (b)   ~ 
the    same   concrete   kept  in  a  damp  condition? 

7.  Draw  a  curve  to   show  the   ititial  and   secant  moduli  of  elasticity 
for   concrete   in  compression. 

3*       l<7hat   is  the  average  modulus  of  elasticity  for  2000   Ib.   concrete? 
9.       What   is  the  approximate  ivorking   stress  used  for  2000   Ib*   concrete? 

10.  In  an  ordinary    structure  what  percentage   change   in  length  can 
be  expected  in  concrete  during  hardening? 

11.  If  the  amount  of    steel  in  an  unloaded  reinforced  concrete 
member   is  greater  than  1.5$,  v/hat    stress  may  be  produced   in 
the   concrete   if   it  becomes  thoroughly  dry? 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 
Cor re spondence  Cour  se  s 

Materials  of  Engineering  Construction 

Civil  Engr.-8B       Assignment  17.       Professor  C.  T.Wiskocil 
PERMEABILITY  AND  ABSORPTION  OF  CONCRETE 

Read  Articles  523  to  552  inclusive*   Impermeable  concrete 
is  required  in  the  construction  of  basements,  tunnels,  and  subvrays, 
and  of  tanks  for  the  storage  of  liquids,  \7aterproof  is  the  term 
more  commonly  used  to  designate  concrete  which  prevents  the  passage 
of  water  through  it.  Leaks  not  only  defeat  the  purpose  for  which 
impermeable  concrete  is  intended  but  permit  the  entrance  of  sea 
water,  alkalies,  and  frost,  all  of  which  affect  the  durability  of 
concrete.   If  concrete  is  properly  proportioned,  mixed,  placed  and 
cured,  it  'is  possible  to  secure  a  finished  product  that  will  be 
impermeable  under  water  pressure  up  to  and  exceeding  that  produced 
by  a  100  foot  head.  If  the  structure  is  liable  to  crack,  water- 
tight expansion  joints  must  be  provided  or  the  use  of  waterproof 
membranes,  as  described  in  Article  538,  must  be  resorted  to. 

Read  Article  523,  v/hich  explains  the  difference  between 
absorption  and  permeability.  Mote  that  the  statement  is  made  that 
there  is  no  relation  between  these  properties.  Both  are  important. 
Absorption  is  easily  determined  but  permeability  can  be  determined 
only  by  the  use  of  an  elaborate  arrangement  to  test  the  specimen, 
and  even  this  does  not  always  work  satisfactorily. 

Read  Article  524.  The  principal  types  of  permeability  specimens 
are  illustrated  on  page  483.  The  main  cause  of  trouble  in  tests  of 
this  kind  is  leaks  particularly  at  high  pressures,  uhile  several 


Fngr.-8   Materials  of  Engineering  Construction   Assn.  17, page  2. 

types  of  specimens  are  illustrated  there  is  no  accepted  standard 
and  moreover  tais  test  is  not  frequently  made. 

With  increasing  proportions  of  cement,  other  variables 
remaining  constant,  the  imperineabilit/"-  of  concrete  increases-   See 
Article  525. 

Figure  16  on  page  486  and  figure  9  on  page  464  show  that  the 
density  of  concrete  affects  its  permeability  more  than  it  does  the 
strength.  &  porous  concrete  might  have  considerable  strength  and 
yet  be  very  permeable  to  water. 

The  use  of  insufficient  mixing  water  makes  the  placing  of 
concrete  difficult  and  usually  results  in  a  pouous  product.  An 
excessive  amount  of  water  produces  a  large  amount  of  water-voids 
and  decreases  the  density.  The  most  impervious  concrete  is  made 
from  a  plastic,  workable  mix.   See  Article  527. 

The  one-minute  mix,  recommended  by  the  Joint  Committee  previously 
referred  to,  is  undoubtedly  sufficient  to  insure  homogeneity  of  mix 
and  will  therefore  produce  impermeable  concrete,  providing  that  the 
aggregates  are  well  graded  and  the  correct  amount  of  cement  and 
mixing  water  are  used.  With  these  latter  conditions  properly 
provided,  insufficient  mixing  will  cause  permeability;  but  it  is 
obvious  that  two  or  more  minutes  of  mixing  will  not  be  able  to 
overcome  deficiencies  in  mix,  grading  of  aggregates,  or  amount  of 
water  used,  and  will  not  under  these  conditions  produce  an 
impermeable  concrete.  Read  Article  528. 


Engr.-8   Materials  of  Engineering  Construction.  Assno  17, page  3« 

Permeability  as  vrell  as  strength  of  concrete  are  greatly 
affected  by  improper  curing.   Inherent  impermeability  is  destroyed 
by  allowing  concrete  to  dry  out  at  early  ages.  Concrete  must  be 
kept  damp  in  order  to  cure  properly.   See  article  489. 

I!inor  factors  vhich  influence  the  permeability  of  concrete 
are  given  in  Article  550.  They  are  relatively  unimportant. 

The  degree  of  absorption  holds  a  prominent  place  in  all 
specifications  for  quality  of  concrete  products.  Not-withstanding 
its  importance  it  has  not  been  thoroughly  investigated*  Read 
Article  531. 

The  A.3«  T.M. Standards  for  testing  cement-concrete  seTrer 
pipe  for  absorption  state  that  the  test  spscimen,  a  piece  of  broken 
pipe,  shall  be  heated  for  not  less  than  3  hours  at  a  temperature  of 
not  less  than  110  degrees  Centigrade  (230°  Fahrenheit).  The  specimen 

is  than  cooled,  weighed  and  placed  in  water  which  is  brought  to 
the  boiling  point  and  boiled  for  five  hours.  After  the  water  has 
cooled  to  room  temperature  the  specimen  is  removed  and  the  superficial 
moisture  i-'iped  off.  The  specimen  is  then  veighod  and  the  per- 
centage absorption  calculated  on  the  basis  of  the  dry  weight. 

As  indicated  in  the  first  paragraph  of  Article  531,  the 
excessive  drying  of  the  specimen  undoubtedly  increases  the  absorption. 

In  a  recent  report  issued  by  the  Structure.!  Materials  Research 
Laboratory,  Lewis  Institute,  Chicago,  the  absorption  of  concrete 
i-ras  studied,  'while  it  was  not  determined  in  accordance  with  the 
A.  S.T.1,1,  specifications,  various  factor  s  which  influence  absorption 


Engr.-8  Materials  of  Engineering  Construction.  Assn.  17,  page  4. 

were  studied  and  the  results  should  be  of  value*  The  following 
are  the  principal  conclusions: 

1.  The  absorption  of  concrete  was  reduced  by  using  coarser 
aggregate s,  so  long  as  the  concrete  was  plastic.  The  absorption  of 
concrete  made  vrith  aggregate  graded  0  -38  (fineness  modulus  of  1*8) 
7/as  about  5/£,  v/hile  for  OD  ncrete  vrith  aggregate  graded  0-1  1/2  inch 

(fineness  modulus  6.0)  the  absorption  was  reduced  to  <%• 

2.  The  absorption  of  concrete  -;:as  reduced  by  increasing  the 
quantity  of  cement. 

3.  Ths  absorption  was  increased  as  more  mixing  water  was  used. 

4.  The  storage  of  concrete  in  a  moist  place  immediately  after 
molding  decreased  the  absorption.  The  longer  the  concrete  was  kept 
moist  the  lower  the  absorption. 

5.  In  general,  in  concrete  of  high  strength  there  was  lo^ 
absorption. 

'WATERPROOFING 

Read  Articles  522  to  £38  inclusive.   In  many  cases  concrete 
is  poorly  proportioned,  mixed,  placed  and  cured,  and  in  such  instances 
it  is  necessary  to  close  up  the  pores  in  order  to  make  the  concrete 
impermeable.   In  nost  instances  it  would  be  cheaper  to  make  good 
concrete  than  to  resort  to  the  use  of  waterproof ing  materials. 

The  principal  method  of  filling  the  pores  is  by  the  addition 
of  inert  and  active  fillers.  They  are  listed  in  Article  532.   Some 
are  added  to  the  mixing  water  while  others  are  dry  powders  and  are 
added  to  the  cement. 


Engr.i-8       Materials  of  Engineering  Construction.     Assn.    17, page  5« 

The   statements  made  in  Article  533  on  the  effect  of  hydrate 
lir-e    should  be    seriously  questioned.     According  to  EFFECT  OF 
BYLRATED  LUvE  AND  OTHER  POWDERED  ADMIXTURES  IS  CONCRETE  by  Duff 
Abrams,  Bulletin  8  of  the   Structural  Materials  Research  Laboratory, 
Lev-is  Institute,    Chicago   (Dec.    1S20):    (a)  Ifydrated  lime  as  an 
adniixture  reduces  the  compressive    strength  of  concrete     of  all  mixes 
and  consistencies,    (b)  The  reduction  of  concrete    strength  is  nearly 
proportional  to  the  quantity  of  hydrated  lime  used,      (c)  Rich 
concrete  mixtures   show  a  greater   loss  in   strength  due  to  hydrated 
lime  than  lean  ones. 

If    shrinkage  cracks  occur   or   construction  joints  are  not  veil 
made  the   integral  fillers  will  not   keep  out  the  water.      Surface 
treatments  are  resorted  to.     In  general  they  are  not  very   successful. 
Sylrester's  trash  of   soap  and  alum  is  described  in  Article  537. 
Other  treatments  are  hot  paraffin,   bituminous  materials  and  rich 
mortar. 

The  most  positive  method  of  waterproofing,  but  the  most  expensive, 
is  the  use  of   layers  of  v/aterproof  membranes  laid  on  the   surface 
of  the  concrete    subjected  to  water  pressure.     Tarred  felt,  burlap 
and  canvas  are    some  of  the  membranes  used.     They  are   cenented  to 
the  concrete  with  various  bituminous  materials.      See  Article  538. 
EFFECTS  OF  TEMPERATURE   ON  CONCIiETE 

The  effect  of   low  temperature  on  fresh  concrete   is  explained 
in  Articles  539    to    542   inclusive-      It  is  a  well   krxnvn  fact  that 
heat  hastens  the    setting  and  hardening  of  concrete  and  that  cold 


Engr.-8   Materials  of  Engineering  Construction.  Assn.  17, page  6. 

delays  it.   Low  temperature  produces  an  appreciable  effect  below  50 
degrees  Fahrenheit  and  becomes  more  effective  in  retarding  the 
phenomena  of  setting  and  hardening  as  it  decreases,  until  the  freezing 
point  of  -water  is  reached.  Below  this  temperature,  fresh  concrete 
will  freeze. 

?i/hen  water  is  added  to  portland  cement  a  chemical  reaction  occurs 
which  evolves  heat  of  sufficient  quantity  to  raise  the  temperature 
of  fresh  concrete.  Under  favorable  conditions  the  rise  in  temperature 
is  greatest  in  the  period  from  6  to  12  hours  after  mixing. 

If  concrete  is  to  be  subjected  to  low  temperatures  it  is 
important  that  it  acquire  all  possible  strength  at  an  early  age. 

It  is  the  general  opinion  that  freezing  temperature  will  not 
injure  concrete  that  has  had  an  opportunity  to  harden  at  least  48 
hours  under  favorable  conditions.  Alternate  freezing  and  thawing 
at  an  early  age  may  cause  injury. 

Concrete  should  be  protected  from  the  elements  for  at  least 
12  hours  after  being  poured  during  which  time  the  heat  from  the 
chemical  action  accelerates  hardening  and  retards  the  later  cooling. 

Light  structures  with  thin  sections  need  more  protection 
than  concrete  poured  in  large  masses.  Furthermore,  since  the 
circulation  of  air  hr,s  a  marked  effect  on  the  cooling  of  heated  bodies; 
fresh  concrete  should  be  protected  frora  wind. 

The  diffusivity  of  fresh  concrete  of  the  usual  mixes  i£ 
•0063  in  e.g.  s.  units.  This  constant  expreesses  the  rate  of  flow 
of  temperature.   It  is  a  function  of  the  density,  specific  heat  and 


'TV/ 


Engr.-8     Materials  of  Engineering  Construction.     Assn.    17, page  7* 

thermal  conductivity.     The  emissivity  of  fresh  concrete   is  the 
rate  of   lo^s  of  heat  by  radiation,   convection,   and  evaporation 
of    surface  -v/ater.      In  c.g.s.   units  its  average  value   is  «046. 
These  values  have  been  determined  by  Tokujiro  Yoshida.   -.vho  has 
also  prepared  various  cooling  diagrams,   thus  affording  data  which 
perinit  calculations  of  the  time  required  for   concrete  to  reach 
freezing  or  any  other   given  temperature  under   knovm  conditions  of 
initial  temperature, mass  and  atmospheric  temperature  of  the  concrete, 
and  the  amount  of  protection  given  it  after   it  is  poured* 

Heating  of  materials,  which  is  an  excellent  method  of  ensuring 
early  hardening  and  delaying  the  fall   in  temperature,    should, 
not  be  carried  above   100  to  120  degrees  Fahrenheit. 

If  the  temperature  of  the  concrete  over  a  given  period  is 
kno'vn,   the  comparative    strength  may  be  estimated  from  Figure   15  in 
INFLUENCE  OF  TEMPERATURE  ON  TEE  STRENGTH  OF  CONCRETE  by  A.B. 
lucDaniel,   Bulletin  81,   of  the  Engineering  Experiment   Station, 
University  of   Illinois.     This  is  an  aid  in  deciding  on  the   safe  time 
to  remove  forms  when  the  temperature   is  low. 

The  three  methods  of  concreting  in  cold  v:sather  are:  heating 
the  materials,  placing  protective   coverings  over  the  poured  concrete, 
and  the  use  of  chemicals  to   lo^er  the  freezing  point.      Calcium 
chloride,    see  Article  542,    is  being  used  to  accelerate  the    setting 
of  concrete  at  low  temperature,   even  on  large  and  important  work. 
Part  of  the     410,000  cu.  yds.   of  concrete  on  Ontario's  Niagra 
Pov/er  Development,   according  to  an  article  by  Blanchard  and  Young^ 


Engr.-8   Materials  of  Engineering  Construction.  Assn. 17, page  8. 

in  the  Engineering  News-Record  of  April  6,  1922,  page  554,  was 
poured  in  *.  eesing  weather.  Two  and  one  half  percent  of  calcium 
chloride  was  used  end  due  to  the  acceleration  it  caused  in  the 
hardening,  the  forms  were  stripped  in  12  hours.  It  is  interesting 
to  note  that  all  this  concrete  was  scientifically  proportioned 
to  meet  a  definite  strength  requirement  at  28  days. 

Actual  practice  and  laboratory  experiments  have  demonstrated 
the  value  of  calcium  chloride  in  highway  construction  to  such  an 
extent  that  the  Highway  Department  of  the  state  of  Illinois,  during 
the  past  year  (1921)  has  allowed  its  use  for  accelerating  the  setting 
of  concrete  in  cold  weather  construction.  They  also  have  spread 
it  over  the  usual  concrete  pavement  to  accelerate  the  setting  under 
normal  conditions.   It  was  applied  3  to  16  hours  after  the  concrete 
had  been  poured.  About  3  lb»  were  used  per  square  yard  of  surface. 
Experiments  have  proved  that  the  hardening  effect  occurs  during  the 
first  24  hours  the  salt  is  on  the  concrete. 

Calcium  oxychloride,  known  as  Cal,  is  readily  soluble  in 
voter,  in  which  it  decomposes  into  calcium  hydroxide  and  calcium 
chloride.   It  is  a  dry  white  powder  and  is  not  hygroscopic, like 
commercial  calcium  chloride.  Portland  cement  mortars  treated  with 
Cal  and  stored  in  air,  attained  at  2  days  a  strength  greater  than 
that  of  untreated  mortars  at  28  days.  Three-year  tests  by  the 
Bureau  of  Standards  on  concrete  gaged  with  a  solution  of  calcium 
chloride  are  sufficient  grounds  for  believing  that  the  addition  of 
Cal  vrill  not  injuriously  affect  the  ultimate  strength  and  durability 


Engr.-S     Materials  of  Engineering  Construction.     Assn.   17,  page  9. 

of  portland  cement  concrete. 

The  effect  of  high  temperatures  on  concrete.-     Read  Article 
54:5.     VJhile  concrete   is  a  good  fire  resistant  material,   ranking 
•with  burnt  clay  products  such  as  brie!'  and  terra  cotta,      it  77111 
actually  fuse  and  be  destroyed  v,rhen  exposed  to  high  temperature  So 
The  temperature  at  which  average   concrete  t/ill  fuse   is  about  2,200 
degrees  Fahrenheit.    It  probably  varies   slightly  with  the  brand  of 
cement  .and  the  type  of  aggregates  used.     Fused  concrete  has  been 
found  in  ruins  of  hot  fires   such  as  those  of  the  Edison  plant,  the 
chemical  plant  of  the  Barrett  Manufacturing  Co.,    in  1920,  and  the 
Seamless  Rubber   Company's  plant  in  1921,    in  which  highly  inflammable 
liquids  caused  the  high  temperatures.      Such  temperatures  are 
generally  not  encountered  but  they  are  possible  even   in  ordinary 
structures.      In  the  fire  in  the  office  building  of  the   Chicago , 
Burlington  and  Quincy  Railroad   Co.   in  Chicago,  March  1922, 
temperatures  in  excess  of  2,000  degrees  Fahrenheit  were  reached. 
These  temperatures  were  undoubtedly  confined  to  relatively   small 
areas.      It   is  interesting     to  note  that  -while  the  contents  of  the 
building  within  these  areas  were  completely  destroyed,   the  concrete 
adequately  protected  the    steel  frame  of  the  building.     There  rvas  a 
certain  amount  of    spalling. 

About  2   1/2  inches,  of  concrete   is  generally   considered   sufficient 
thickness  of  fireproof ing  for   steel  work.     Reinforced  concrete 
columns   should  have  2    inches,  vhile  floor    slabs  are  adequately 
protected  vrith  1  inch  of  concrete. 


Engrc-8       Hater  i:. Is  of  Engineering  Construction.     Assn»17,page   10. 

It  has  "been  observed  that   concrete  made  with   silicious  aggregates 
is  not  as  resistant  to  fire  as  concrete  made  with  limestone,  trap 
rock,   and  "burnt  clay  aggregates*     The  distinct  advantage   in  the  use 
of  concrete  to  fireproof   steel  is  that   its  expansion  and  contraction 
-re  nearly  the    same  as  those  of   steel   (see  Article  544),   and  the 
spelling  action (under  heating  and  cooling)   is  therefore,   reduced 
to  a  minimum. 

Other  thermal  properties  given  in  Article  545  are  relatively 
unimportant.     Recent  tests  by  Carman  and  Nelson  give   .0037  as  the 
average  thermal   conductivity  for  average     concrete;    see  Table  26 
on  page  503   in  the  text. 

DURABILITY  OF  CONCRETE 

Read  Articles  546  to  550  inclusive.     The  reliability  of 
existing  information  on  the  disintegration  of   concrete  by  alkali  is 
questionable.     This  statement  does  not  apply  to  that  given  in 
publications  listed  at  the  end  of  Article  547  in  the  text,    since 
these  contain  v/ithout  question  the  most  important   contributions 
on  the    subject  at  the  present  time.      Other   investigations  have  been 
made  but,   taken  as  a  trhole,   the  results  of  these   investigations  and 
tests  are  not  conclusive. 

The  most   import-ant  examples  of  failure  of  concrete  which  have 
been  reported  are   in  Canada.     The  articles  announcing  these  failures 
describe  only  the  extent  of  disintegration  and  attribute  the  cause 
to  alkali  because  of  its  presence   in  the    surrounding   soil.     In  no 
instance  do  they  give  the  history  of  the  concrete,  %?hich  may  have 


Engr.-8   Materials  of  Engineering  Construct  ion .  Assn.  17, page  11. 

been  a  lean  mixture,  or  made  of  poorly  graded  aggregates,  or  sand 
with  orgaric  matter  in  it;  or  which  again,  may  have  been  poorly 
mixed  or  made  with  an  excess  amount  of  water.  Any  of  these  conditions 
would  yield  a  concrete  of  low  durabii^ ty  or  resistance  to  weather- 
ing. The  Winnipeg  aqueduct  is  probably  the  most  important  structure 
which  shov;s  disintegration  but  there  are  many  other  concrete 
structures  which  are  satisfactorily  withstanding  forces  similar 
to  these  which  seem  to  be  disintegrating  this  structure.  The 
subject  is  important  and  is  at  present  being  thoroughly  investigated 
by  the  Portland  Cement  Association  v/ith  other  engineering  societie  s 
and  interested  engineers. 

Structures  of  concrete  and  reinforced  concrete  have  shown  partial 
disintegration  under  the  action  of  sea  water,  frost,  •  rnd  stray 
electric  currents,  as  well  0.3  alkali.   They  have  usually  been  made 
of  porous  concrete  or  ure  of  such  shape  that  they  crack  under  the 
action  of  the  loads  which  come  upon  them,  so  that  the  water  entering 
the  concrete  can  exert  its  disintegrating  influence.  Well  made 
concrete  thut  has  been  properly  cured  has  not  been  affected  by  these 
disintegrating  agencies.  The  materials  and  methods  to  be  used  in 
order  to  secure  good  concrete  have  been  discussed  in  previous 
assignments. 

Portland  cement  products.-  Read  Articles  551  to  561  inclusive. 
Concrete  blocks  were  probably  the  first  product  in  the  pre-cast  con- 
crete industry.  As  a  whole  they  were  poorly  made  and  fashioned  after 
an  imitation  of  rock-faced  stone.  The  inferior  quality  of  the 


Engr.-8       Materials  of  Engineering  Construction-  Assn  17,  page   12. 

product,   \7hich  was  a  poor   imitation  of  cut    stone,   caused  the  early 
failure  of  the  industry.     At  the  present  time,  however,   architectural 
concrete    stone  is   successfully  competing  vrith  natural   stone  for  the 
facing  and  trimming  of  buildings.      Important  examples  of    such 
construction  are  found  on  the  campus  of  the  University  of  California 
at  Berkeley,    in  the   case  of  Hilgard  EaXl  and  Gilman  Hall.     The 
color   combinations  in  Hilgard  Hall  are  particularly  pleasing.     The 
color   designs  were  executed  in  what  is  knoivn  as  scraffito.     Pre-cast 
trim  and   scraffito  offer  a  permanent  material  that  is  relatively 
inexpensive   (when  compared  -.vith  natural   stone)   and  *;nLll  undoubtedly 

VV&  OJai    ifc    cva'tniefciftv      «&      JW*4/  UvUftu     JW      U  Ctvtfc     (U^iM*1*'1 

be  used  in  the   construction  of  other  buildings     on  the   campus.*    Most 
pre-cast  trim  is  made  by  the  dry  cast  method  in  \?hich   specially 
prepared  molds  are  used.     The  product  is  immediately  removed  from 
the  molds,  pointed-up  7;here  defective  in  surface  finish,   and   set 
aside  to  cure.      Considerable  care  must  be  taken  in  curing  these 
products-     Concrete   stone  is  also  m^.de  by  pressure  and  wet  oast 
methods.     The  American  Concrete   Institute  has  given  the  name  concrete 
architectural   stone  to  this  product. 

Concrete  pipe   is  another   important  pre-cast  product.     The 
cost  of  manufacture  depends  largely  upon  the  method  of  manufacture. 
Under  present  methods  of  manufacture  a  very    satisfactory  product  is 
being  made.     The  principal  difficulty  in  the  use  of  pre-cast     concrete 
pipe  for  pressure  purposes  is  the  joint. 


Engr.-8     1,'laterials  of  Engineering  Construction-     Assn.  17,  page   13. 

QUESTIONS. 

!•   Define  impermeability.  I/hat  is  its  relation  to  absorption  as 
applied  to  concrete? 

2.  What  are  the  two  methods  used  to  determine  permeability  of  concrete? 

3.  \7hat  are  the  principal  causes  for  permeable  concrete? 

4.  V.'hat  are  the  principal  causes  for  high  absorption  in  concrete? 

5.  V/hat  is  the  most  effective  method  of  xraterproofing  concrete? 

6.  Y/hat  factors  affect  the  length  of  time  it  takes  fresh  concrete 
to  cool  in  freezing  vreather? 

7.  ?*'hat  is  the  mininum  tin©  that  fresh  concrete  should  be  kept 
at  a  temperature  favorable  to  hardening? 

8.  What  is  the  temperature  at  which  concrete  Trill  fuse? 

9.  Are  temperatures  necessary  to  fuse  concrete  ever  reached 
when  buildings  are  destroyed  by  fire? 

10.  What  are  some  of  the  causes  of  the  disintegration  of  concrete? 

11.  Discuss  the  effect  of  sea  water  on  the  durability  of  concrete. 

12.  "What  are  the  principal  portland  cement  products? 

13.  HoTr  are  pre-cast  concrete  products  cured? 


r  •  •• 


• 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials   of  Engineering  Construction 
Civil  Engr-SB.  Professor  C.T.   Wiskocil 

Assignment   18. 
METALS  AND  THEIR  ORES 

Read  Articles  562  to  568   inclusive.      This  chapter   is  an 

introduction  to  the   study  of  metals  which  is  now  to  be  taken  up. 
That  part   of  Article   564  which  describes  certain  metals  may  be 
omitted  at  this  time  because   it  must  be  reviewed   later   in  the  course 

when  these  metals  are   discussed   in  detail. 

Since  this  chapter   is   introductory   it   is  relatively  unim- 
portant.     The   essential  parts  will  be  discussed    later. 

Article-    563   lists  the   important  base  metals  used    in 
engineering  construction.     They  are   iron,   copper ,  .lead }   and   zinc. 
Aluminum  is  an  importpnt  metal  of  secondary  rank.      Iron  and 
aluminum,    in  the    list  given  belov/,   are   small   in  percentage,   but 
are   found    in  abundant   quantities. 

Average  composition  of  earth's  crust 


Oxygen 

47.05 

Phosphorus 

0.11 

Silicon 

28.26 

Sulphur 

.11 

Aluiainum 

7.98 

Florine 

.10 

Iron 

4.47 

Barium 

.097 

Calcium 

3.45 

Manganese 

.077 

Magnesium 

2.34 

Chlorine 

.06 

Potassium 

2.50 

Chromium 

.033 

Sodium 

2.54 

Strontium 

.033 

Titanium 

0.45 

Zirconium 

.025 

Hydrogen 

0.16 

Nickel 

.023 

Carbon 

0.13 

Vanadium 

.018 

Civil  Engr-8B.  Assignment  18.  page  2. 

Read  carefully  the  first  paragraph  of  Article  564. 

An  ore  may  be  said  to  be  a  mineral  or  a  mixture  of  minerals 
from  which  one  or  more  elements  may  be  extracted  with  profit.  As 
indicated  in  Article  565  it  is  seldom  that  a  deposit  consisting  of 
but  a  single  mineral  is  encountered. 

Read  carefully  *l;s  article  on  the  principles  of  extraction 
of  metals,  Article  568»  This  brief  outline  of  principles  will  be 
useful  when  the  methods  are  studied  in  detail. 

REDUCTION  OF  IRON  FROM  ITS  ORES 

Iron  Ores  and  Ore  Deposits:-  The  reading  assignment  covers 
Articles  569  to  573  inclusive. 

Read  Article  569  on  the  economic  importance  of  iron  and 
steel  and  review  the  paragraph  on  iron  in  article  564,  previously 
referred  to.   Iron  is  sometimes  referred  to  as  the  master  metal. 
No  other  one  metal  has  contributed  so  much  to  our  welfare  and  com- 
fort. There  is  scarcely  an  artiale  we  use  that  is  not  produced 
from  iron  or  by  means  of  it.  There  is  no  exact  substitute  for  it, 
The  automobile  and  the  railroad  could  not  have  been  developed 
without  it. 

The  native  sources  of  iron  ores  that  are  being  exploited 
at  the  present  time  are  listed  in  Article  570.  As  the  United 
States  becomes  more  densely  populated  the  deposits  in  the  western 
states,  such  as  those  now  known  to  exist  in  Colorado,  Utah,  New 
Mexico,  Idaho  and  Montana,  will  be  developed. 

The  Lake  Superior  district  is  the  most  important  ore  region 


Civil  Engr-8B.  Assignment   18.  Page  3. 

in  the   Qnited   States.      It   is  made  up  of   isolated  bodies   of  ore 
surrounding  Lake   Superior.     These   ore   Dodies   or  ranges  are   scat- 
tered   over  Michigan,  Wisconsin,    Minnesota  and   Ontario   '^in  Canada;. 
The  Marquette   range   is   in  Michigan,   along  the   shore   of  Lake   Superior 
It  was  discovered   in  1844  and   operation  was  begun  in  1854.     The 
ere   is  principally  red  hematite,   and   small  amounts   of  magnetite 
and    limonite.     The  Menominee   range,   also   in  iiichigan,  was   opened   in 
1872.      It   is  composed  mainly  of  hematite.     The  Gogebic  range   is 
partly  in  Michigan  and   partly   in  Tn/isconsin.      It  was   opened   in  1884. 
The   ores  are  mostly  dklv^rated   hematites  which  are  red   in  color  and 
rather   soft.      The  Vermillion  range,  which   lies   in  Minnesota,  ras 
opened   the   same  year  as  the  Gogebic   range.      The   ores  are  hard 
hematites   of  red  and  blue  color.      These   ranges  constitute  the   old- 
est group.     The   latest   ranges   opened,   the  Missabe   in  1892  and 
Cuyana   in  1911,   are  the  most   important.      The  greater   part   of  the 
ore  used   in  the  production  of  pig   iron  today  comes  from  the 
Missabe   range.      It   lies   in  Minnesota,   and  yields   soft  hydrated  hema- 
tites and    limonites.     The  deposits  are  comparatively  shallow,      xhe 
Guyana   range  also   lies    in  Minnesota.      i\^ny   of  the   ores   in  this  range 
contain  manganese  and  are   mined   for  their  manganese   content   only. 
Some  have  as  much  as  45?£  of  manganese.     Both  underground     and   open- 
pi*   mining   is  carried    en  in  the   Superior  District.      Most   of  the 
mining  on  the  Missabe   range   is  done  with  steam  shovels. 

The  Birmingham  district   is   second    in   importance   of  the   Lake 
Superior  district.      It   is   in  Alabama.      The   ore    is  a  variety  of  red 


Civil  Engr-3  B  .  Assignment    18.  page  4. 

hematite  and    occurs  with  shale,    sandstone  and   some   limestone. 
Most   of  the  mines  now  being   operated   are  worked   by  underground 
me^hods        On  account   of  the   proximity   of   ore,    limestone,    and   coal 
suitaole   for  making  coke,   this  district  has  an  advantage   over   other 
districts   in  the   country.      The   ore  usually  contains  about    .8% 
phosphorus.      Tne  duplex   or  triplex  process   is  employed  and  a   slag 
•with  a  high  phosphorus  content   is   obtained  when  the  pig  iron  is 
purified-      This   slag   is   used  as  a  fertilizer. 

Grouped  according  to  chemical  composition  the  chief   iron 
bearing  minerals  are  the   iron  oxides,    iron  carbonates,    iron  sili- 
cates and   iron  sulphides.      Only  the   oxides  are  a  factor   in  the 
manufacture   of  steel  in  the  United   States. 

In  Article  571  the    iron  ores  are  considered   in  order   of 
their    iron  content. 

Magnetite     is  ferro-ferric   oxide.      It   is  found   in  Arkansas 
and   Nev:   Jersey,   as  well  as   in  the    states   named    in  Article   571. 
Its  magnetic   property   is  made  use    of   in  the    location  of  ore   oodies 
below  the   surface   of  the   ground   and    in  mechanically  purifying  the 
the    ores,   by  magnetic   concentration. 

Hematite      is  anhydrous  ferric   oxide,  FeO-?-      It  furnishes 


the  base   of  the  world's  most   important   ores.      Hematite   ores  are 
widely  distributed  and  vary   in  iron  content;   the   principal  ones  are 
red   hematite,    specular  hematite,    oolitic   hematite   and   fossil   ore. 

Limonite      is  a  hydrous   ferric   oxide.      The   group  of   ores 
from  turgite   to   lirnonite  varies   in   iron  content  from  66  to  52f0. 
The  formula  for   limonite  and    its   iron  content   is  given  in  the  text. 


Civil  Engr-8  B  .  Assignment   18.  page   5. 

These  minerals   are  widely  distributed  throughout  the  United  States. 
In  Virginia  tney  make  up  the  greater  part   of  the  availaole   ores. 

Siderite ,   a  ferrous  carbonate,    is  the  principal  ore   in  the 
car  Donate   group.      It   is   sometimes  called   kidney  ore,    spathic    iron 
ore,    or  blackoand.      It   is  not  a  commercial  ore   in  the  United  States 
bnt   is   important   in  England.      The    ores  of  the  above  divisions  are 
usually  calcined   before  they  are  charged    into  the  blast  furnace. 

The  manufacture   of  pig   iron:-       Reading  assignment,  Articles 
574  to  584   inclusive. 

While  the   purple   of  this  part   of  the  assignment   is  to  dee 
scribe  the   manufacture   of  pig  iron,   a  fev;  remarks   on  the  history 
of   iron  T>;ould  be   of  interest  %t  this  point.      The  date   of  the  first 
use   of  iron  is  not  known.     Archaeological  research  has  determined 
that   it  has  been     in  use  through  a  period   of  only  about  4,000  years. 
Since   iron  corrodes  and  therefore   leaves  no  trace,    it   is  difficult 
to  find   evidence   of  its  early  use.      Doubtful  evidence  exists  to 
show   its  use    in  the   construction  of  the   pyramids  about  4000  B.C. , 
but    its  use  by  the  Assyrians  about    1500  B.C.      and    later  by  the  Greeks 
is  more  certain.      The  Romans  became  quite   proficient   in  the  use   of 
metallurgy,  as   is   shov»n  uy  their  •weapons.     The  Britons  had   some 
knowledge   of   iron  before  the  Roman  occupation  of  England  under 
iC-aesar-     At  that  time   iron  v;as  probably  produced  by  heating  ore  and 
charcoal   in  a   flat   bottomed   forge   until  a   small  body   of  pasty  metal 
was   obtained  -which  could  be  hammered  and  worked    into  wrought   iron. 
A  process   similar  to  this  7/as  used   in  Europe  until  about   1350.     At 


Civil  Engr-8  B.          Assignment  18.  Page  6. 

this  time  there  was  first  used  a  crude  blast  furnace  in  which 
was  produced  an  iron  that  could  be  cast.   The  blast  furnace 
method  was  improved  in  England  in  1619  by  the  use  of  coke  instead 
of  charcoal  as  the  fuel.  Aoout  200  years  later  the  hot  blast  -was 
introduced.  The  first  American  iron  -works  was  operated  in  Vir- 
ginia in  1619  and  the  first  blast  furnace  was  built  about  100 
years  later.   The  most  important  advances  in  blast  furnace  con- 
struction and  operation  began  to  be  made  about  1880. 

The  reduction  of  iron  ore  to  pig  iron  is  brought  about  by 
alternate  layers  of  ore,  fuel,  and  flux  in  proper  proportions 
through  a  specially  designed  opening  into  the  top  of  a  blast  fur- 
nace (a  tall  vertical  stac.i:  ,  lined  with  fire  brick) ,  while  hot 
air  is  blown  into  the  bottom  of  the  furnace.   The  nitrogen  and 
the  products  of  combustion  pass  upward  through  the  furnace  and  es- 
cape at  the  top.   At  periodic  intervals  impurities ,  in  the  form 
of  slag,  are  drawn  off  near  the  bottom  and  molten  metal  is  re- 
moved through  a  tap-hole  in  the  hearth.   In  early  furnaces  the 
metal  was  cast  in  sand  molds  which  were  arranged  in  rows  and  re- 
sembled a  litter  of  pigs;  hence  the  metal  was  called  pig  iron. 

The  operation  of  a  blast  furnace  is  continuous,  one 
charge  following  another  without  a  creak.   Since  iron  ore  is  gen- 
erally an  oxide  it  must  be  deoxidized  or  reduced  in  order  to 
obtain  metallic  iron.   Carbon  is  the  reducing  agent  and,  in  the 
form  of  coke,  it  is  used  as  fuel.   During  the  reducing  process  the 
iron  absorbs  carbon  so  that  pig  iron  has  a  high  carbon  content. 


Civil  Engr-8  B-  Assignment   18.  Page  7. 

Coke   is  the  principal  fuel  used   in  the  manufacture   of  pig 
iron.     Anthracite  coal  anc:   charcoal  are   used  to  a   limited  extent. 
Coke   is  the  residue   of  the  destructive  distillation  of  bituminous 
coal.      For  blast  furnace  use   it  must  be  porous,    so  as  to  be 
readily  burned,   and   strong  so  as  to  withstand  the   load   of  the   ore 
and   other  materials  above   it  without  crushing.      The  by-product   or 
retort  process  for  making  coke   is  rapidly  replacing  the  bee -hive 
process.      In  the   latter  process  air   is  admitted    into  the  coking 
chamber  and  the  products   of  distillation  are  burned  and  thus  wasted, 
In  the  by-product  process  the  coking  chamber   is  air  tight  and  heat 
is   supplied  to  the   outside  to  coke  the  coal.      The   products   of 
distillation  are   recovered.      These  products  are  hydrocarbon  gases, 
tar  and  ammonia.     The  method   of  manufacture  has   little  effect  on 
the  quality  of  the  coke. 

Smelting   is  a  metallurgical   operation  in  which  metal,    in  a 
state   of  fusion,    is   separated  from  impurities  with  which   it   is 

combined.      It   involves  two  processes,    one,   the  reduction  of  the 
metal,   and  the   other,   the   separation  of  the  metal  from  the  mix- 
ture.    These   operations  are  facilitated  by  the  use   of  a  flux.      The 
primary  function  of  the  flux   is  to  render  the  materials  more 
readily   fusible   and   the   secondary   function   is  to  supply  a   substance 
with  which  the  elements   originally  combined  with  the  metal     may 
combine.      The  flux  should  be   free  from  impurities   such  as  sulphur 
and   phosphorus.      The  materials  to  be   fluxed   determine   the   character 
of  the   flux.      If  they  are  basic,   an  acid    flux  must  be   used.      In 
most   ores,   however,   the    impurities  are  acid    so  that  the   predomina- 


Civil  Engr-3  B.          Assignment  18  Page  8. 

ting  flux  is  basic,  basic  fluxes  are  limestone  and  dolomite.   In 
the  smelting  zone  of  the  blast  furnace  the  flux  combines  with  the 
gangue  to  form  slag.   Slags  furnish  the  means  by  v;hich  impurities 
are  separated  from  the  metal  and  removed  from  the  furnace.   In 
the  blast  furnace  the  slag,  on  account  of  its  fusibility  and  dis- 
solving power ,(  forms  the  only  positive  method  of  removing  sulphur. 
Slag  has  a  lew  density  and  floats  upon  the  metal.   It  protects  the 
metal  from  the  hot  gases  and  prevents  overheating  and  at  the  same 
time  conserves  the  heat  in  the  metal.   Since  it  has  the  power  of 
dissolving  oxides  it  keeps  the  metal  clean  and  also  facilitates 
the  separation  of  impurities  from  the  molten  metal. 

The  modern  blast  furnace  and  its  accessories  are  illustrated 
in  Figure  1  on  page  534.   Be  able  to  sketch  the  cross  section  of 
a  blast  furnace.  Be  sure  to  shov;  the  double  Dell-hopper  at  the 
top. 

The  beet  practice  today  in  blast  furnace  construction  is 
represented  by  furnaces  from  90  to  100  ft.  high  (see  the  informa- 
tion at  the  bottom  of  page  533  in  the  text).   In  these  furnaces, 
the  hearth  or  crucible  is  about  10  ft  high.   The  bosh  zone  is  from 
10  to  12  ft.  high,  and  the  stacK  70  ft.  or  more. 

Be  able  to  describe  the  operation  of  the  hot  stoves.  The 

air  is  heated  to  about  1000  degrees  Fahrenheit  in  the  stoves  and 

»   0 
forced  into  the  furnace  through  tuyeres  (pronounced  twe~  yar  )  at 

abcut  15  Ib.  per  sq.  in.  pressure.   The  temperature  in  the  blast 
furnace  varies  from  a  maximum  of  about  3500  degrees  F»  at  a  point 
just  above  the  tuyeres  to  about  500  degrees  F.  at  the  stack  line, 


Civil  Enpr-8  B.  Assignment   18.  Page   9. 

at  tne  top  of  the   furnace.      The  efficiency  of  the   furnace   is  greatly 
increased  by  the  use   of  preheated  air. 

The  greatest   single   improvement   in  blast  furnace   operation 
since  Neilson's  hot  blast   is   James  Gay ley's  dry  blast  process.      It 
has  been  estimated  that   in  the   summer  months  a  furnace  which  uses 
40,000  cu.    ft.    of  air  per  minute  will  take   in  with  this  amount   of 
air  about  225  gal.    of  water  per  hour.      It   is   obvious  that  this 
water  will  reduce  the  efficiency  of  the  furnace.      In  Gay ley's 
process,   the  moisture   is  removed   from  the  air  by  drawing  it   over  a 
system  of  pipes  coded  with  brine  which  in  turn  is  cooled  with 
liquified  ammonia.     The  moisture   is  condensed  and   frozen  on  the 
pipes.,    leaving  the  air  practically  dry.      This   is  a  refrigeration 
process.     The  dry  air    is  forced  through  the  hot   stoves  and  then  in- 
to the  furnace.      In  spite   of  the  advantage   of  the  dry  blast   it  is 
still  most  common  practice  to  use  undried  air.      It   is  probable, 
however,   that  the  dry  blast  will  soon  become  as  universally  used 
as  Neilson's  hot  blast. 

The  amount   of  materials  used  by  a  modern  blast  furnace   in 
24  hours   is  very   impressive.     These  are   given  in  the   last  paragraph 
of  Article  578  on  page   535.      It   is  evident  that  even  a  single  unit 
plant  means  a   large  production  which  necessitates   large  working 
capital. 


Civil  Engr-   8  B 


assignment   18.. 


page   10. 


BIASH 

> 

i 

i       MATERIAL 

9000  #s 

^ 
\ 

^       CHAINED 
\ 

Limestone  1200jjte~ 

Coke     2000  #s 

Iron  Ore  4000  #s 

Tunnel  Head 

mat  5i 

Gases 
12,360  #s 

\ 

1 

.- 

V 

HITERIA.L 
S        PRODUCED 

Slag^     1600  $s 

Pig   iron     2240  #s 

"ial  charged   and   produced    in  making   < 

of  pi'g   iron. 

This  represents  American  olast  furnace  practice   in  the 
northern  district. 

If  pib  iron  is  to  be  used    in  the  production  of  steel   it   is 
transferred  to  the  converters   or   steel  furnaces   in  the  molten  con- 
dition if  they  are  near  by.     When  the  blast  furnace   is  not  part   of 
the    steel  plant   it   is  necessary  to  cast  the  metal   into  pigs  and 
transport   it   in  that  condition.      The   old  method  was  to  use   sand 
molds,    from  the  arrangement   of  which,   as  has-oeen  stated,   pig   iron 


Civil  Engr-8  B.  Assignment   18.  page   11. 

got    its  name.      The  present  method    is  to  use  casting  machines.     These 
are  an  endless  chain  of  buckets   lined  with  fire  clay  which  receive 
the  molten  metal  as   it  comes  from  the   blast  furnace  and  dump  the 
solidified   pigs   into  cars.      The   length  of  the  bucket   line   is  such 
that  the    iron  has  time  to  solidify  before  the  bucket     is  dumped. 

Blast  furnace   slag   is  run  off  into  slag  cars  and  dumped   on 
the  waste   pile   or  granulated  with  a   stream  of  water  and  used   later 
in  the  manufacture   of  port  land  cement,     A.  stream  of  vrater   is  more 
effective  than  dumping  the   slag   into  a  body   of  water.      Some   slag  is 
used   for  ballast  for   railway  tracks  and   some    in  the     manufacture   of 
mineral  7/ool;  most   of  it,   however,    is  wasted. 

Fig   iron  itself   is  not. a   structural  material.     When  remelted 
and   cast   into  molds   it    is  called  cast   iron.      Cast   iron  forms  the 
basic  material  for  the  manufacture   of  steel. 


Civil  Engr-8  B.  Assignment   18.  Page  .112.. 


QUESTIONS 


1.  Where  are  the  principal  iron  ore  deposits  in  the  United  States? 

2.  What  are  the  principal  iron  ores?  Give  the  miner a logical  name 

and  the  approximate  iron  content  in  tabular  form. 

3.  Outline  the  process  of  manufacture  of  pig  iron* 

4.  What  is  pig  iron?  Why  is  it  called  pig  iron? 

5.  What  is  a  flux?  Why  is  a  flux  used  in  the  manufacture  of  pig 
iron? 

€.   Of  what  use  is  slag  in  the  process  of  smelting? 

7.  Sketch  the  cross  section  of  a  blast  furnace,  give  the  approxi- 
mate dimensions  and  name  the  essential  parts. 

/ 

8.  What  are  the  two  recent  improvements  in  blast  furnace  operation 
which  have  greatly  increased  its  efficiency? 

9.  How  much  raw  material  is  charged  into  a  blast  furnace  to  pro- 
duce a  ton  of  pig  iron? 

10.  What  are  the  principal  changes  involved  in  the  production  of 
pig  iron  from  the  iron  ore? 

11.  What  are  the  requirements  for  blast  furnace  coke? 


i 


UNIVERSITY   OF  CALIFORNIA.  EXTENSION  DIVISION 

Correspondence  Courses 
Materials   of  Engineering  Construction 
Cixil  Engr-8  B.  professor  C.T.   Wiskocil 

Assignment   19. 
TrE   MANUFACTURE   OF  YiROUGHT    IRON 

Introduction:-         Read  Articles  585  and   586.      In  the  blast 
furnace   operation  the  metal  absorbs   large  amounts   of  carbon  which, 
together  with  other   impurities,   render   it  too  brittle  and  coarse 
for   structural  use.     .all  the  methods  used  to  refine  pig  iron  are 
essentially  processes  for  the  removal  of  the  carbon  by  means  of 
oxidation.       As  sty  own  in  Article  586,   carbon  is  the   only  impurity 
that   is  removed   in  the   form  of  a  gas.      Other   impurities  are  taken 
up  by  the   slag  and   separated  from  the  metal   in  that  way. 

Before   large-scale   production  of   steel  was  possible,  wrought 
iron  was  the  most    important  metallic   structural  material.      it  was 
rolled    into  various   shapes,  •which  were  used   in  the  construction     of 
buildings,   ships,   bridges  and   structures   of  all  kinds.      It  had 
sufficient   strength  besides   it*  toughness  and  ductility.     Further- 
more  it  was  easily  forged.      These   properties  made   it  more  adaptable 
than  cast   iron.      it  was  used   for  tools  and   implements  that  did  not 
require  a  tempered   edge.      The  development  of  the  Bessemer  and   open- 
hearth  processes  for  making  steel  occurred    in  the   latter  part  of 
the  nineteenth  century;   since  that  time   steel  has  replaced  wrought 
iron  as  the  principal  structural  material.     Wrought   iron     is   still 
extensively  used   for  general  blacksmith  work,  and   for  water  and 


-*'-  •'  '**-"•••  «• 


Civil  Engr-8  B.  Assignment   19.  page  2. 

gas  pipes,  because   of  the  belief  that  it  resists  corrosion  better 
than  steel,      it   is  also  used  for  rods  and  bolts  which  are  to  be 
subjected  to  impact   or   shock  because   of  the  belief  that  this 
material,  with  its  fibrous  structure,    is  more  resistant  to  shock 
than  steel.     Wrought   iron  has  failed  to  compete   successfully  with 
soft   steel  chiefly  on  account   of  the  high  cost   of  labor.     The 
process  of  manufacture   is  most  laborious  and  yet  requires  consider- 
able  skill.     The   skill  gained  by  experience   in  the  process  is 
superior   to  a  theoretrical  knowledge   of  it.     These  conditions  make 
it  difficult  to  obtain  men  since  the   intelligence  required  could 
obtain  higher  rewards   in  other  pursuits. 

The   International  Association  for  Testing  Materials  defines 
wrought   iron  as   "malleable    iron  which  is  aggregated  from  pasty 
particles  without   subsequent  fusion,   and  containing  so  little  car- 
bon that   it  does  not  harden  usefully  when  cooled   suddenly." 
Bradley  Stoughtor.'s  definition  is,    "Wrought   iron  is  almost  the   same 
as  the  very   low-carbon  steel  except  that   it   is  never  produced  by 
melting  and  casting   in  a  mold  but   is  always  forged  to  the  desired 
size   and  form.      It  usually  contains   less  than  0.12^  of  carbon.      Its 
chief  distinction  from  the    low-carbon  steels   is  that   it   is  made  by 
a  process  which  finishes   it   in  a  pasty,    instead   of  a   liquid  form 
and   leaves  about   1  to  2  7£  of  slag  mechanically  disseminated  through 
it," 

The  puddling  process.--       Read  Article  588.      In  the  manufac- 
ture  of  wrought   iron,   a  special  grade  of  pig  iron  known  as  forge  pig 
is  used.      It   is  high  in  silicon.      The   silicon  is  desirable   since 


Civil  Engr-8  B.  Assignment  19.  Page  3. 

it  aids  in  the  formation  of  sufficient  slag  to  cover  the  bath  and 
prevent  excessive  oxidation  of  the  iron.  Phosphorous  and  sulphur 
must  be  kept  low  since  they  are  not  completely  removed  with  the 
slag. 

Basic  iron  oxides  are  used  to  fettle  the  hearth.   Iron  ore 
is  frequently  used  to  line  or  fettle  the  furnace.  The  position  of 
the  fettling  material  is  shown  in  Figure  1  on  page  544.  During 
the  boiling  stage  the  carbon  unites  with  the  oxygen  supplied  mostly 
by  the  fettling  material  and  later  by  the  air  passing  over  the 
bath.  The  slag  mu'st  be  strongly  basic  at  this  stage  so  that  it 
will  retain  the  phosphorous  and  sulphur. 

Slag  is  never  completely  removed  in  the  squeezing  process* 
It  is  always  present  in  wrought  iron  in  the  form  of  fibers  which 
extend  in  the  direction  of  rolling.  This  is  the  distinguishing 
characteristic  of  wrought  iron.   It  can  be  detected  by  etching  a 
polished  surface  with  acid.  Under  the  microscope  the  structure  is 

clearly  revealed,  as  shown  in  Figure  1  on  page  598.  The  nick-bend 

T^eMAtVy 
test  is  also  used  to  d^te^t  wrought  iron.  The  piece  of  metal  is 

cut  partly  through  and  then  bent.  The  fibrous  structure  will  be 
shown  by  this  test. 

The  classes  of  wrought  iron  are  given  in  Article  589. 
Charcoal  irons  are  the  purest  grades  of  wrought  irons.  They  are 
used  in  the  manufacture  of  electrical  apparatus  and  boiler  tubes, 
as  well  as  for  those  purposes  listed  in  Article  589.  Wrought  iron 
costs  more  than  low-carbon  steel.   It  is,  therefore,  sometimes 
adulterated  with  steel  scrap.  The  scrap  and  the  wrought  iron  are 


. 
V     P-:-;:       .     •••    ...-,     .         I*  hV>.    .         i: 


Civil  Engr-8  B.  Assignment  19.  Page  4. 

piled  together  and  brought  to  a  welding  temperature  and   rolled 
into  merchant  bars.     The  product   Is  sold  as  wrought   iron.     This 
material  should  not  be  confused  with  the  charcoal  or  knobbled   iron 
described   in  the  text.     Read  Article  589. 

THE  MANUFACTURE   OF  STEEL 

Introduction:-     Read  Article  590.      It   is  not  possible  to  give 
a  concise  definition  of  steel.     Probably  the  most  satisfactory  one 
is  that  given  by  R.M.   Howe.      "Steel  is  that  form  of  iron  which  is 
malleable  at   least  in  some  one  range  of  temperature,  and   in  addi- 
tion is  either   (a)  cast  into  an  initially  malleable  mass;   or  (b)   is 
capable   of  hardening  greatly  by  sudden  cooling;   or   (c)   is  both  so 
cast  and  so  capable  of  hardening.11         Cast  iron  and  pig  iron  are 
not  malleable  but  chrome  and  manganese  steels  are  malleaole   only 
through  a  short  range  of  high  temperatures;  at  ordinary  temperatures 
they  are  not  malleable.     The  condition  in  (a)   distinguishes  steel 
from  malleable  oast   iron,  which  is  made  malleable  by  special  treat- 
ment after   it   is  cast.     Wrought  iron  is  not  cast  and   it  cannot  be 
hardened  by  sudden  cooling.     Cementation  steel   (see  page  656)   is 
not  cast,  but   it  will  harden  upon  sudden  cooling;  there  are  also 
many  carbon  steels  which  are     cast  but  will  not  harden.     These  facts 
will  show  why  it   is  difficult  to  define   steel. 

Iron  oxide  and  air  are  available  for  the  purification  of  pig 
iron.     The   oxide  of  iron  is  the  principal  substance  used   in  the  manu- 
facture of  wrought  iron.      Iron  ore  and  air  ar«  the   oxidizing  sub* 
stances  used   in  the  manufacture   of  steel  but  they  require  different 


•  . 


• 


s  » 

••«  . 


Civil  Engr-8  3.  Assignment  19.  Page  &• 

kinds  of  apparatus.  The  two  chief  methods  of -purification  are  the 
pneumatic  and  the  open  hearth.  In  both  methods  the  purification 
may  be  accomplished  by  oxidation  alone,  in  which  c§se  they  are 
called  acid  processes.  If  oxidation  is  carried  on  in  the  presence 
of  strong  bases  the  process  is  known  as  the  basic  process.  In  the 
acid  process,  only  carbon,  silicon,  and  manganese  are  removed  from 
the  iron.  In  the  basic  process,  in  addition  to  these  elements,  the 
phosphorus  is  also  removed.  The  pig  iron  produced  in  this  country 
is  best  adapted  to  treatment  by  the  basic  open  hearth  and  the  acid 
Bessemer  process.  These  are  the  leading  methods  used  in  the  manu- 
facture of  steel. 

The  Bessemer  process  of  making  steel;-   Read  Articles  591 
to  595  inclusive.   This  process  consists  essentially  in  blowing  air 
under  a  pressure  of  20  Ib.  per  sq.  in.  through  a  bath  of  molten 
iron  contained  in  a  specially  constructed  vessel  known  as  a  convert- 
er. The  silicon  and  manganese  combine  with  oxygen  and  form  a  slag 
while  the  carbon  forms  Co  and  COg  and  passes  out  of  the  bath.  The 
heat  required  to  maintain  the  temperature  of  the  bath  is  obtained 
from  the  chemical  action  which  occurs  when  the  elements  are  oxidized 
Steel  made  in  this  way  contains  oxides  which  render  it  unfit  for 
use.  A  recarburizer  must,  therefore,  be  added  after  the  metal  is 
blown  to  give  it  the  necessary  strength  and  toughness.   The  process 
is  explained  in  detail  in  Article  593;  study  this  article  carefully. 

The  mixer  described  in  Article  593  and  illustrated  in  Figure 
3,  on  page  548,  is  very  important  in  the  Bessemer  process.  Besides 
acting  as  a  storage  place  for  hot  metal  as  indicated  in  the  text 


•    -i    •;*•;'                          •                             ••::•'  -'t               '  •  -3  '     'I1'"  •',    I    '•     •  '• 

1    •       "  '   "          '  - ...>.!.. 


I    ..-•/'.    -.  • ;.  '.      .,  • 
3j     -.-;         J   •:    :•  :.'  .      . 


Civil  En5r-8  B.  Assignment   19.  page  6. 

:  conserves  the  heat   in  the  molten  metal  and  makes  the  charge 
taken  to  the  converters  more  uniform.     Mixers  average   in  size  from 
200  to  1200  tons  capacity. 

Pig  iron  suitable  for  the  manufacture   of  steel  by  the 
pneumetic   process   (acioj   should  contain  3  to  4$  carbon,   1  to  1.5$ 
silicon,    less  than  Q.lf0     phosphorus,   and   small  amounts  of  sulphur 
and  manganese. 

Basic  Bessemer   is   successful  only  with  pig  iron  which  -is 
high  in  phosphorus  and   low   in  silicon.     There  are  practically  no 
ores  mined   in  the  United  States  that  are  high  enough  in  phosphorus 
for  the  basic  Bessemer  process.     Pig  iron  with  too  much  phosphorus 
for  the  acid  Bessemer   is  made   into  steel  by  the  basic   open  hearth 
process. 

The  Siemens  process  of  making  steel:-       Read  Articles  596. 
to  598   inclusive.     The  process   is  described   in  detail  and   is  very 
important. 

There   are   several  distinct  modifications     of  the  basic   open 
hearth  process.     There    is  the  pig-and-ore  process,   the  pig-and- 
scrap  process  and  the  ail-scrap  process.      The  pig-and-scrap  process 
is  now  in  most  general  use.     When  pig  iron  is  expensive,  as  it  is 
out  here   on  the  Pacific  Coast   on  account   of  high  transportation 
charges,   the  all-scrap  process   is  most  economical.     The  mills  in 
the  bay  region,    such  as  the  Pacific  Coast  Steel  Company  at  South 
San  Francisco,   the   Judson     Steel  Company  at  Emeryville,   and     the 
Columbia  oteel  Company  at  Pittsourg,  all  use  the  all-scrap  process. 


Civil  Engr-8  B.  Assignment  19.  Page  7. 

The  basic  open  hearth  method  is  employed  and  a  high  grade  of  steel 
is  produced.  The  nearest  blast  furnace  is  at  Pueblo,  Colorado. 

Remember  that  the  recarburization  of  basic  steel  cannot  be 
accomplished  in  the  furnace  because  the  carbon,  silicon  and  manganese 
in  the  recarburizer  would  reduce  the  phosphorus  in  the  slag  and  re- 
store it  to  the  metal.  For  this  reason  the  recarburizer  is  added 
to  the  metal  in  the  ladle.  Since  the  recarburizer  cannot  convenient- 
ly be  molten,  it  must  be  ferro-rnanganese  instead  of  the  spiegeleisen 
which  is  used  in  the  acid  open  hearth  process. 

Study  Article  599.   In  it  is  a  summary  of  the  two  most  im- 
portant processes  for  making  steel. 

Read  Articles  600  and  601.  A  method  by  which  the  acid 
Bessemer  and  the  basic  open  hearth  processes  are  combined  is  de- 
scribed in  the  latter  article.  This  process  is  known  as  the  duplex 
process.   It  is  used  extensively  in  the  south  where  the  ore  has  a 
high  phosphorus  content. 

Read  Articles  602  to  604  inclusive  on  the  minor  methods  of 
making,  steel. 

The  manufacture  of  blister  steel  or  cementation  steel  is 
described  in  Article  602.  This  steel  is  very  expensive  but  is  of 
high  quality.  The  cementation  process  has  never  been  used  to  any 
great  extent  in  the  United  States.  The  cementation  process  re- 
sembles the  case  hardening  process  used  to  give  wrought  iron  and 
soft  steel  a  hard  surface  of  high-carbon  steel.   See  Article  710 
in  the  text. 


-•     • 


••     -•' 


Civil  Engr-8  B.          Assignment  19.  Page  8 

The  manufacture  of  crucible  steel   is  described  in  Article 
603.  This  method  of  making  steel  is  widely  used  when  a  high  grade 
product  is  wanted.   Obviously  crucible  steel  cannot  be  made  in 
large  quantities.  This  steel  is  superior  to  open  hearth  and 
pneumatic  steel  because  it  is  made  in  closed  vessels  out  of  con- 
tact with  the  air.  Crucible  steel  is  less  expensive  than  blister 

steel. 

Electric  steel:"  Study  Article  604.  The  Stassano  furnace 

is  of  the  radiation  arc  type.  From  an  electrical  standpoint  this 
furnace  has  the  important  advantage  of  uniform  power  consumption. 
Only  small  sized  Stassano  furnaces  have  been  built  and  are  not 
in  wide  use. 

The  induction  type  of  furnace  was  adapted  to  the  manufacture 
of  steel  by  Kjellin.   It  is  impossiDle  to  obtain  high  temperatures 
in  this  type  of  furnace,  hence  it  is  not  adapted  for  desulphuriz- 
ing operations  in  which  sulphur  is  removed  as  sulphide.  The 
Heroult  furnace  of  the  arc  resistance  type  heads  the  list  of 
electric  furnaces  in  use  for  the  manufacture  of  steel. 

The  following  information  was  taken  from  a  paper  by  Keeney 
and  Lyon,  of  the  United  States  Bureau  of  Mines:   "For  many  years 

all  high  grade  steels  were  manufactured  by  the  crucible  process  but 
since  the  advent  of  the  electric  furnace  there  has  been  a  gradual 

adoption  of  that  furnace  for  refining  steel.   For  the  complete 
refining  of  the  higher  grades  of  steel,  the  use  of  the  electric 
furnace  is  now  thoroughly  established.  Any  products  that  cen  be 


. 


Civil  Engr-8B -  Assignment  19.  page  9. 

made  by  the  crucible  process  can  be  made  by  the  electric  process, 
and  in  most  cases  with  cheaper  raw  materials  and  at  a  low  cost. 
In  the  electric  furnace  complex  alloy  steels  can  be  made  with  pre- 
cision.  The  hig;h  temperatures  attainable  facilitate  the  reactions, 
and  alloys  need  not  be  used  so  largely  for  the  purpose  of  removing 
gas.  Very  low  carbon  steel  can  be  kept  fluid  at  the  high  tempera- 
tures. Steel  free  from  impurities  and  of  great  value  for  electri- 
cal apparatus  can  be  made.  With  the  electric  furnace  large  cast- 
ings can  be  made  from  one  furnace,  whereas  in  the  crucible  process 
steel  from  several  crucibles  must  be  used.  For  small  castings, 
which  require  a  very  high  grade  metal  free  from  slags  and  oxides, 
electrically  refined  steel  is  especially  adapted.  The  electric 
furnace  gives  a  metal  of  low  or  high  carbon  content  as  desired, 
hot  enough  to  pour  into  thin  molds,  and  steel  free  from  slags  and 
gases. 

"Recent  experiments  show  that  electric  processes  have  the 
following  advantages  over  acid  Bessemer  and  basic  open  hearth 
methods,    A  more  complete  removal  of  oxygen;  the  absence  of 
oxides  caused  by  the  addition  of  silicon,  manganese,  etc.;  the 
production  of  ingots  of  8  tons  and  smaller  that  are  practically 
free  from  segregation;  the  reduction  of  the  sulphur  content  to 
.005^  if  desired;  and  the  reduction  of  the  phosphorus  to  .005$c, 
but  with  the  complete  removal  of  the  oxygen." 

Considering  the  various  methods  of  making  steel,  the  process 
in  which  the  electric  furnace  is  used  in  connection  with  the  basic 


• 


.'" 


' 


Civil  Engr-  8  B  Assignment  19.  Page  10. 

open  hearth  will  yield  the  greatest  amount  of  'steel  \vith  highest 
efficiency  "and  quality  of  product. 

The  assigned  subject  is  thoroughly  covered  in  the  text, 
Chapter  XVIII,  and  it  should  be  carefully  studied  since  it  is  very 
important.  The  following  questions  cover  only  a  few  of  the  im- 
portant point's.  You  should  be  able  to  answer  similar  questions  x* 

on  the  other  points  in  the  chapter. 


Civil  Lngr-8  B-  Assignment   19,  page   11, 

QUESTIONS 


1.  What    is  the    importance    of  wrought   iron  as  a   structural 
material? 

2.  Define  wrought   iron. 

3.  Describe  "briefly  the   process  by  which  "wrought   iron  is  made. 

4.  What   is  the   source   of  the    oxygtn  required  to  purify  pig  iron 

in  the   p-ucl  cling  process? 

5.  Why   is   it   necessary  to  have  a  basic   slag? 

6-     What  tests  are  used  to  distinguish  wrought  iron  from  soft  or 
or   lov -carbon  steel? 

7,  Why  is  wrought   iron  sometimes  adulterated  with  steel  scrap? 

8.  Whe.t  are  the   leading  methods  of  making  steel  in  the  United 
States? 

3.  Describe  briefly  the  pneumatic  process. 

10.  What   is  a   recarburizer  and  why  is  it  used? 

11.  Why   is  the  basic  Bessemer  process  not  used   in  the  United  States? 
12  Sketch  the   cross   section  of  a  converter. 

13.   What  are  the   principal  chemical  changes  that  take  place  during 
tiie   open  hearth  process   of  making  steel? 

•  14«   Why  are  different  furnace    linings  used  for  the  acid  and  basic 
processes? 

15.  When  is  the  recarb"»-izer  added   in  the  basic  process  and  "why? 

16.  Compare   the   pneumatic  and   the   open  hearth  processes  for  making 
steel  by  tabulating  the  advantages  and  disadvantages. 

•  17.  Why  is  crucible    steel  more     expensive  than  open  hearth  or 

Bessemer   steel? 

•  18.   Why  is   it  that  a  higher  grade   of  steel  can  be   obtained  by  the 

crucible   process  than  by  the  Bessemer  method? 

19.  What  are  the  advantages   of  the   electric   furnace   in  the  manu- 
facture  of  steel? 

20.  Why  does  the  electric   furnace  produce  a  higher  grade   of  steel 

na^>     Via»*«+  Vi     r>v /•»/» e  e «  9 


UNIVERSITY  OF  CALIFORNIA.  EXTENSION  DIVISION 
Correspondence  Courses  • 

Materials  of  Engineering  Construction 
Civil  Engr-8  B»  Professor  C-T.  Wiskocil 


Assignment  20. 
THE  MANUFACTURE  OF  IRON  AND  STEEL  SHAPES 

Study  Article  605  to  616  inclusive. 

Methods  of  shaping  steel:-    Read  Article  605.  The  next 
step  in  the  manufacture  of  steel,  after  the  refinement  of  the  cast 
iron,  is  to  make  it  into  the  various  shapes  and  forms  required  by 
the  uses  to  which  it  is  to  be  put.   The  shaping  is  a  process 
either  of  casting  or  of  mechanical  working.   Since  steel  is  usually 
in  a  molten  state  after  being  refined,  it  would  appear  that  cast- 
ing vjould  be  the  nost  economical  method  of  shaping  it.  But  metal 
cast  from  the  molten  state  has  an  inherent  lack  of  strength  and 
ductility  when  compared  with  similar  metal  which  has  been  mechanic- 
ally worked  into  shape.  Some  shapes  are  so  intricate  in  form  that 
they  must  be  cast  and  in  others  no  great  strength  is  required  so 
that  casting  is  a  regular  method  employed  for  shaping  many  steel 
products.  The  chief  causes  of  weakness  in  steel  castings  are 
blow  holes,  segregation,  and  crystallization.  These  defects  can 
be  minimized  by  proper  methods  of  manufacture  and  the  use  of 
alloys  is  resorted  to  so  that  steel  castings  can  be  made  of  rela- 
tively high  strength  and  quality  of  metal. 

The  mechanical  v/orking  of  steel  can  be  carried  out  by  three 
different  methods;  namely,  hammering,  pressing,  and  rolling.  Ham- 
mering and  pressing  are  frequently  classed  together  as  forging. 


Civil  Engr-8  B.  Assignment  20.  Page  2. 

i 

Steel  is  probably  more  widely  used  in  rolled  shapes  than  in  any 

other  form.   Steel  plate  for  tanks  and  boiler  shells;  structural 
shapes,  such  as  I-beam* ,  channels  and  angles;  bolts,  nuts,  rivets, 
nails,  rails,  wire,  chain;  and  tubing  and  pipes  are  some  of  the 
products  made  from  rolled  steel. 

Steel  ingots:-  Read  Article  606.  Steel  ingots  for  roll- 
ing or  forging  usually  weigh  from  3  to  10  tons.  The  average  life 
of  an  ingot  mold  is  about  100  heats. 

During  cooling,  ingots  naturally  develop  certain  defects. 
The  principal  defects  are  mentioned  in  this  article.  They  are 
pipes,  blow  holes,  segregation,  and  crystallization.  Other  de- 
fects, such  as.  checks,  scabs,  and  slag  inclusions,  are  incidental. 

Pipes  are  caused  during  the  solidification  of  the  metal, 
as  described  in  the  text.  The  size  of  the  pipe  in  Figure  2  on 
page  560  is  rather  larger  than  usual.  Pipes  are  caused  where  the 
surface  of  the  metal  becomes  oxidized  so  that  it  will  not  weld 
up  in  rolling;  when  thi.p  occurs  :  v.-';  the  pipe  appears  as  a  defect 
even  in  the  smallest  section  into  which  this  part  of  the  ingot  may 
be  rolled.   Pipes  are  liable  to  cause  accidents  in  rolling.  The 
only  way  of  dealing  with  the  pipe  is  to  crop  the  ingot  and  dis- 
card the  part  which  includes  the  pipe.   This  method  causes  con- 
siderable waste  and  various  schemes  have,  therefore,  been  devised 
to  overcome  the  pipe  without  having  to  crop  the  ingot.  The  most 
promising  is  the  hot-top  mold.   The  idea  is,  to  .putt  it  briefly, 
to  keep  the  top  of  the  mold  molten  and  thus  prevent  the  formation 
of  the  pipe.   In  the  ordinary  mole  the  top  is  the  first  to  solidify. 


Civil  Engr-8  B.  Assignment  20.  page  3. 

To  .Tjaice  the  top  the   last  to  freeze  the  upper  part  of  the    ingot   is 
Ljade    larger,   anc  the  upper  part   of  the  mold   is  made  thinner.     A 
different  method,  whicb  has  been  used  to  a  limited  extent,   is  that 
in  which  the    ingot   is  compressed  while  the   interior   is  molten. 
This  also  tends  to  prevent  the  formation  of  the  pipe. 

Blow  holes  are  another   serious  defect.     The   illustration 
(Figure  2,    on  page  560)    is  again  slightly  inaccurate.     The   surface 
cavities  are  very  small,  while  the  deep  seated  blow  holes  are 
frequently   large.      The   latter  may  be   over  an  inch  in  diameter. 
While  the  holes  just  beneath  the   sicin  of  the   ingot  may  be  micro- 
scopic  in  size  they  are,   nevertheless,  the  most  troublesome.     They 
are  nore   lia&le  to  develop  oxidiaed   surfaces  and  thus  to  produce 
seams   in  the   finished   products.     The  deep  seated   holes  are  not 
subject  to  oxidation  and   since  they  tend  to  reduce  the   size   of  the 
pipe  they  are  not  harmful.      The  method   of  compressing  the   ingot, 
previously  referred  to,   prevents  the  formation  of   large  blow  holes 
as  well  as  pipes,   but  it   is  expensive.      It   is  not  "widely  used,   be- 
cause    the  cropping   of  the   ingot   is  after  all  more  economical. 
The  metal  discarded   in  cropping  is  used   in  the   refining  process  as 
steel  scrap.      Steel  that  has  been  properly  made  and  deoxidized  at 
the  time   of  recarburization  will  not  have  troublesome  blow  holes. 
Molten  steel  which  is  not  properly  deoxidized,   and  from  which  gas 
is  bubbling,    is  known  as  wild   steel.     Aluminum  is  very  effective 
in  quieting  or  killing  wild   steel  and   it  does  not  affect  the 
properties   of  the    steel.      The  killing  is  done   in  the    ladle.      Steel 
should  be  quiet  before   it   is  poured. 


Civil  Engr-3  B.          Assignment  20.  page  4. 

Electric  steel,  on  account  of  its  being  refined  without 
contact  with  air  currents  is  particularly  free  from  blov;  holes. 
Segregation  is  the  localization  of  the  impurities  in  the  ingot. 
The  ingredients  in  the  molten  ^netal  have  different  freezing 
points.   The  substance  with  the  lowest  freezing  point  will  be 
located  near  the  top  and  center  of  the  ingot,  about  at  the  bottom 
cf  the  pipe.   Segregation  cannot  be  overcome  but  it  can  be  mini- 
mized by  rapid  cooling. 

Coarse  crystalline  structure  or  ingotism  is  inherent  in 
netal  that  is  cooled  s lovely  from  a  high  temperature.  The  size  of 
the  crystals  depends  upon  the  rate  of  cooling.   Large  crystals 
make  the  ingots  likely  to  tear  in  rolling.  The  rolling  process 
refines  the  grains  and  prevents  the  effects  of  coarse  crystals 
showing  up  in  the  finished  product,  if  it  has  been  properly  worked 

A.  mold  having  a  rough  surface  causes  resistance  to  the 
natural  contraction  of  the  cooling  metal  and  produces  checks  or 
small  cracks  in  the  ingot  skin.   If  the  ii:old  is  improperly  poured 
so  that  the  metal  is  splashed  against  the  sides  of  the  cold  mold 
•where  it  sticks  anc  oxidizes,  the  ingot  •will  have  scabs  on  its 
surface  after  it  is  stripped.   These  defects  produce  a  seamy  pro- 
duct.  In  plates  they  will  form  surface  defects. 

Slag  inclusions  may  be  formed  by  dirt  in  the  ladle  or  mold, 
or  slag  may  be  formed  by  the  oxidation  of  the  metal  in  the  ladle. 
Small  slag  inclusions  do  not  have  time  to  rise  to  the  surface  of 
the  metal.   In  the  finished  product,  slag  inclusions  are  the 
source  of  surface  blisters 


Civil  Engr-3  B.          Assignment  20.  Page  5. 

Pipes,  blow  holes,  and  segregations  cannot  be  entirely 
prevented.  Their  bad  effects  can  be  minimized,  howex^er,  by  the 
use  of  aluminum  to  quiet  the  metal  and  by  rapid  cooling.   Since 
slow  cooling  is  necessary  to  minimize  piping,  careful  study  and 
exercise  of  judgment  are  necessary  to  secure  the  best  quality  in 
any  lot  of  steel. 

Heat  treatment  of  ingots  ;-   Study  Article  607.   Ingots  are 
placed  in  the  soaking  pits  in  a  vertical  position.  This  is 
necessary  because  the  ingot  should  be  stripped  as  soon  as  possible 
so  as  to  conserve  the  most  heat  and  also  so  as  to  require  a  mini- 
mum of  extra  he&ting  in  the  soaking  pit.   Since  the  interiors  in 
the  ingots  when  they  are  stripped  are  still  soft  the  ingot  must 
remain  in  the  upright  position  in  which  it  was  cast.   Otherwise 
the  extent  of  the  pipe  may  be  increased  and  its  position  altered. 
The  upright  position  also  exposes  the  greatest  surface  of  the  in- 
got so  that  it  will  more  quickly  come  to  a  uniform  temperature. 

General  method  of  rolling;-   Read  Article  608.  Rolling, 
as  a  method  of  shaping  steel,  is  now  most  extensively  used. 
Kenry  Cort  is  credited  with  having  rolled  the  first  steel  in  1783. 
Other  metals  were  evidently  rolled  before  that  time.  Rolling  is 
a  very  rapid  method  of  shaping  steel. 

In  the  breakdown  of  the  heavy  ingots  large  mills  are  used. 
These  reduce  the  ingots  to  lighter  sections,  in  such  simple  shapes 
as  round,  square,  and  rectangular.  When  the  ingot  is  reduced  to 
a  square  section  six  inches  .In r grr  on  a  side,  or  to  rectangular 
sections  in  which  the  widths  are  less  than  twice  the  thickness, 


Civil  Engr-8  B.          Assignment  20.  Page  6. 

these  sections  are  called  blooms.   If  the  section  of  the  metal  is 
square,  and  between  1  1/4  and  6  inches  on  a  side  it  is  called  a 
billet.   If  in  width  the  section  far  exceeds  the  thickness  it  is 
called  a  slab.  Blooms,  billets  and  slabs  are  cut  into  convenient 
lengths.  Mills  for  the  shaping  of  steel  are  named  after  the  prod- 
uct they  make;   as  olooming  mill  and  slabbing  mill.   In  England 
a  mill  making  blooms  is  known  as  a  cogging  mill. 

Rolling  mills;   Read  Article  609.  The  various  types  of 
mills  are  described  in  this  article.  The  rolls  are  illustrated  in 
Figure  3  on  page  561.   They  are  made  of  cast  iron,  steel,  or 
alloy  mixtures.  Rolls  must  be  tough  to  withstand  the  shock  pro- 
duced as  the  piece  enters  them:  they  must  have  high  transverse 
strength  to  work  under  the  high  pressures  developed  in  rolling; 
they  must  be  hard  so  as  to  have  good  wearing  qualities;  and  they 
must  be  sound  so  that  they  will  not  develop  surface  defects,  and 
thus  cause  the  rejection  of  the  finished  products.  Cast  iron 
rolls  are  known  as  sand  rolls  and  chilled  rolls;  alloy  steel  rolls 
are  given  the  trade  names  of  steel  rolls  and  adamite  rolls. 
Chilled  rolls  are  expensive  but  they  must  be  used  where  a  high 
grade  finish  is  required.  A  higher  tonnage  is  obtained  from  these 
rolls  than  from  any  other  kind.   Chilled  rolls  for  plate  mills 
have  been  made  as  heavy  as  40  tons.  These  require  a  mold  about 
23  feet  in  length.  Besides  being  subject  to  violent  impact  and 
heavy  pressure,  rolls  are  unevenly  stressed,  and  unevenly  heated, 
and  even  over  heated  and  then  suddenly  cooled.   These  are  very 
severe  conditions  and  they  can  be  stood  only  by  well  made  rolls. 


Civil  Engr-8  B.  Assignment  20.  page  7. 

Steel  rolls,  while  they  hava  the  required  strength,  do  not  hold 
their  finish  uncer  the  high  temperatures  of  rolling.  They  are 
seidOiQ  used  for  finishing  rolls,  but  they  are  well  adapted  to  the 
work  of  the  blooming  mills  and  heavy  roughing  stands.  The  adamite 
rolls  have  not  ^et  been  very  Widely  used. 

plates  ;-  Read  Article  610.   Plates  are  rolled  in  an 
ordinary  mill  and  sheared,  as  indicated  in  this  article,  or  they 
are  roilec  in  a  universal  mill.   Plates  are  known  as  sheared  or 
universal  mill  plates,  according  to  the  method  by  which  they  were 
rolled.   Sheared  plates  are  not  suitaole  for  girder  construction; 
universal  mill  plates  with  rolled  edges  are  desirable  for  this 
purpose.   Universal  mill  plates  can  be  rolled  to  exact  and  uniform 
widths  so  that  shearing,  costs  are  reduced,  and  furthermore,  machin- 
ing is  frequently  unnecessary.   Moreover,  universal  mills  turn  out 
great  tonnage  so  that  universal  mill  plates  are  lower  in  cost 
than  sheared  plates. 

Sheets:-   Read  Article  611  on  the  manufacture  of  thin 
steel  sheets. 

Pipes:-  Read  Article  612.   The  manufacture  of  seamless, 
but -welded,  and  lap-welded  tubing  is  explained  in  this  article. 

Wire:-  Read  Article  613;   it  explains  the  manufacture  of 
wire.  Wire  dies  are  made  of  steel  plate  and  chilled  iron.   The 
latter  are  most  extensively  used  in  this  country.  They  are  ex- 
tremely hard. 

Forging  and  pressing :-    Read  Article  614.   Shaping  by 
hammer  forging  is  a  slow  process.   However  it  is  a  simple  one  and 


Civil  Engr-8  B-  Assignment  20.  page  8. 

was  the  first  method  used  to  shape  metals.     The  first  power 
hammer  was  built   in  England  but  the   first   steam  hammer  was  a 
French  invention.      It  was  first  operated    in  1842.      It  was  a  single 
acting  hamraer   in  which  the  head   or  top  was  raised  by  steam.     The 
invention  of  the  double  acting  steam  hammer, which  employed   steam 
power   on  the  downward   stroke,  was  a  decided   improvement.        The 
first   one  was  built   in  Pennsylvania,    in  1888. 

The   suddenness   of  the  hammer  blow  tends  to  localize  the 
effect  and  hence    only  the   exterior   of  the  metal   is  refined.      If 
each  blow   of  the  hammer  reduces  the  metal  to  a  considerable  de- 
gree,   or    if  the  metal   is  thin,  this  method  will  produce  material 
that   is  superior  to  rolled   steel.      Small  objects  made   of  high- 
grade   steel,    such  as  stock  for  cutlery  and  tools,   are  usually 
hammered   into  shape .     The  making  of  drop  forgings   is  explained   in 
the  text. 

Forging  presses  are  an  English  invention  of  about   1860. 
They  were   introduced   into  the  United  States   in  1887.     The  sizes  & 
and  working  pressures  are  g,iven  in  Article  614.     The  action  and 
effect   of  pressing   is  different  from  that   of  hammering.      Pressing 
is   so  slow  that  a     kneading  action  takes  place  and  the   effect, 
therefore,   penetrates  deep   into  the   steel  instead    of  refining  only 
the   surface  as  does  hammering.     Both  methods   improve  the  quality 
of   steel. 

Steel  castings:-     Read  Article  615.      During  recent  years 
there   has  teen  much  development   in  the  quality  of  steel  castings 


Civil  Engr-8  B.  Assignment  20.  Page  9. 

and  also  in  the  types  of  objects  cast.   Large  castings  which  are 
subjected  to  heavy  stresses  are  now  made  of  cast  steel.   Loco- 
motive frames,  stern  frames  for  ships,  anchors,  buckets,  and  bucket 
tumblers  for  gold  dredgers  are  some  of  the  articles  made  of  carbon 
ard  alloy  steels  in  the  form  of  castings.  The  Columbia  steel 
Company  at  pittsburg,  California,  is  the  largest  steel  casting 
plant  on  this  part  of  the  pacific  Coast.  Most  of  their  steel  is 
made  in  basic  open  hearth  furnaces  of  steel  scrap.  They  also 
operate  a  small  acid  open  hearth  furnace. 

The  production  of  good  steel  castings  requires  considerable 
foundry  experience.  Many  complex  foundry  problems  are  involved. 
In  order  to  produce  sound  castings  it  is  necessary  to  have  large 
sink  heads  so  placed  in  the  mold  that  the  hot  steel  is  available 
to  fill  any  part  of  the  casting  where  there  is  a  tendency  on 
account  of  too  rapid  cooling,  to  produce  a  cavity.  Due  to  the 
excessive  shrinkage  of  steel  castings  there  are  severe  internal 
stresses  set  up  in  the  cooled  product.  These  stresses  can  "be 
relieved  and  the  structure  of  the  casting  refined  by  proper  anneal- 
ing.  Steel  castings  must  be  carefully  designed  so  that  there  are 
no  sharp  angles  in  the  outline.  The  molds  for  large  castings 
must  be  well  reinforced  to  withstand  the  heavy  loads  of  molten 
metal. 

Omit  Article  616  on  page  5(qf.   The  statistics  given  in 
this  article  are  not  important. 


Civil  Engr-8  B.  Assignment  20.  Page   10. 

QUESTIONS 

1.  What  methods  are  used  in  shaping  steel? 

2.  How  do  the  various  processes  employed  in  shaping  steel 
affect  its  quality? 

3.  What  is  an  ingot,  a  blooa,  a  "billet? 

4.  What  is  a  pipe?  How  is  it  caused?  Can  its  occurrence  be 
prevented?  How  does  it  affect  the  metal  in  a  rolled  section? 

5.  What  is  segregation  and  how  is  it  minimized? 

6.  How  are  blow  holes  formed?  Can  their  formation  be  prevented? 

7.  What  is  a  universal  mill? 

8.  What  are  the  rolls  of  a  steel  mill  made  of? 

9.  How  is  steel  tubing  made? 

10.  How  are  the  cooling  stresses  in  steel  castings  relieved? 

11.  Why  is  it  necessary  to  soften  wire  during  the  drawing  process? 
How  is  this  softening  accomplished? 


UNIVERSITY  OF  CALIFORNIA.  EXTENSION  DIVISION 

Correspondence  courses     ' 

loiter ials  of  Engineering     Construction 

Civil  Engr-8  B  <  professor  C-T-  Wiskocil 

Assignment  21, 

FORMATION  AND  STRUCTURE  OF  ALLOYS 
Alloys  in  general-.-  Read  Articles  617  to  6266 inclusive* 

Reasons  for  alloying  metals  are  given  in  Article  617.  By 
the  alloying  process,  desirable  properties  may  "be  improved  and  un- 
desirable properties  may  be  lessened „  An  alloy  may  be  tougher, 
harder  or  more  ductile  than  any  of  the  constituent  metals.  The 
cost  of  production  may  be  decreased  by  introducing  cheaper  metal 
into  the  alloy  and  by  producing  an  alloy  that  is  more  easily 
worked  (cast  and  machined)   than  the  metals  from  which  it  is 
made.. 

A  mixture  is  defined  in  Article  618.   In  a  mixture  the 
tiro  or  more  ingredients  do  not  bear  a  fixed  proportion  to  one 

another,  and  however  thoroughly  corn-mingled  maintain  a  separate 
existance^  The  constituents  of  a  mixture  can  alv/ays  be  detect- 
ed by  microscopic  examination. 

As  indicated  in  Article  619,  elements  combine  in  definite 
fixed  proportions  to  form  compounds.  The  formation  of  chemical 
compounds  is  not  of  much  importance  in  the  consideration  of  iron 
and  steel. 

Solid  solutions  are  described  in  Article  620.   The  most 
familiar  examples  of  solutions  are  in  the  form  of  liquids.  How- 
ever it  should  be  remembered  that  every  mixture  of  gases  is  a 

solution 


Civil  Engr-8  B.  Assignment  21.  Page  2. 

and   that  even  metals  may  form  solutions  which,  when  they  solidify, 
are  known  as   solid   solutions.      The   solidification  of  a   liquid 
solution  does  not  necessarily  produce  a   solid    solution.      If  the 
constituents     separate  rr>on  solidifying  the   solid   is  a  mixture. 
In  a  mixture  the    individual  ingredients  may  be   seen  although  in 
some  cases   of  thoroughccccBrciiingling  the  use   of  a  microscope   is  nec- 
essary .     But   if  the  constituents  remain  completely  merged   so  that 
they  retain  in  the   solid   state  the  essential  characteristics  of  a 
solution,   the   solid   is  called  a   solid   solution.     The   solid   solu- 
tion must  possess  such  uniformity  of  structure  that  the  constitu- 
ents cannot  be  detected  by  physical  means  such  as  microscopic 
examination,  and  furthermore  the  combination  of  the  component  parts 
in  any  proportion  must  be  possible.      In  these  regards  it  differs 
from  a  compound-     Glass  is  a  solid   solution;  an  alloy  of  gold  and 
silver   is  another.      In  the   latter  case  the  elements  combine   into 
the   same  kind   of  crystal  no  matter  -v?hat  their   relative  amounts 
may  be . 

Study  Article  €??   carefully.     As  explained    in  this  article 
most  alloys   of   steel  are  formed  by  fusion.      Low  carbon  steels  are 
given  a  hard   exterior   surface  by  the  method   of  diffusion  in  which 
the  diffusing  material  may  be   solid,    liquid   or  gas.     The  term 
miscible     used   in  this  article  means  capa"bldl*-y  of  being  mixed; 
raixable 

Read  Article  622   on  allotropy-     Allotropy  may  be  defined  as 
the  ability  of  an  element  to  exist   in  two  or  more  conditions, 


Civil  Engr-8  B-          Assignment  21.  Page  3. 

which  are  distinguished  by  differences  in  properties.  Carbon, 
for  instance,  may  exist  as  diamond,  charcoal,  lampblack,  and  black- 
lead.   Iron  has  several  allotropic  forms.   See  Article  658  on 
page  590. 

Study  Article  623  on  the  crystalline  structure  of  metals. 

Metals  are  inherently  crystalline,  and  it  is,  therefore,  in- 

» 
correct  to  speak  of  the  crystallization  of  iron  and  steel  as  a 

result  of  fatigue.   See  Article  822,  on  page  771. 

The  strength  and  toughness  of  metals  are  influenced  by 
the  shape  and  size  of  the  crystals  as  well  as  by  the  chemical  com- 
position of  the  metal.   Steel  of  high  strength  has  very  small 
crystals  and  they  can  be  detected  only  under  a  powerful  microscope. 
The  microphotographs  on  pages  596  and  597  will  illustrate  this 
point.  The  effect  of  heat  treatment  on  the  shape  and  arrangement 
of  crystals  is  shown  in  the  illustrations  on  pages  628,  629  and 
630.  Until  recently  the  examination  of  the  fresh  fracture  of  iron 
and  steel  was  the  only  method  of  classifying  the  product.  Even 
at  the  present  time,  melters  in  charge  of  open  .hearth  furnaces 
cast,  break  and  examine  the  fresh  fracture  of  small  bars  of  metal, 
in  order  to  watch  the  elimination  of  the  impurities  from  the  bath, 
and  at  the  end  of  the  heat  to  determine  the  carbon  content,  which 
they  predict  to  within  a  few  points.   If  the  carbon  content  of  a 
piece  of  steel  is  known,  skilled  inspectors  can  determine  approxi- 
mately by  its  fracture  the  heat  treatment  it  has  received,  and  its 
probable  strength  and  toughness. 


Civil  Engr-8  3.          Assignment  21.  page  4. 

As  explained  in  Article  623,  when  steel  passes  from  the 

liquid  to  the  solid  state,  the  molecules  of  the  various  constitu- 

i 
ent£  arrange  themselves  to  form  small  bodies  having  regular 

geometrical  outlines.  This  phenomenon  is  called  crystallization. 
Individual  crystals  may  be  octahedral  or  cubical  bodies,  and  under 
ideal  conditions  of  high  fluidity,  absence  of  foreign  particles, 
slow  cooling,  and  undisturbed  liquid,  will  form  perfect  geometric 
shapes.  However,  under  conditions  of  manufacture,  steel  solidifies 
into  imperfect  crystals  v;ith  irregular  form,  which  are  sometimes 
called  grains. 

Read  Article  62<t  on  the  effects  of  solubility  relations 
in  alloys.   Since  no  examples  are  given  it  may  b^' rather  difficult 
to  comprehend  the  information  given.   If  this  article  is  reviewed 
after  the  study  of  Art  Vies  627  to  636  inclusive,   in  which  defin- 
ite cases  are  taken  up  the  more  general  statements  will  be  under- 
stood. 

Study  Article  625.   Microscopic  examination  and  examination 
of  heating  and  cooling  curves  afford  the  most  important  means  of 
investigating  the  properties  of  pure  metals  and  their  alloys.  The 
method  of  obtaining  cooling  curves  is  explained.   It  should  be 
remembered  that  the  temperature  of  the  material  must  be  observed 
and  recorded  at  uniform  intervals  of  time  during  a  uniform  heating 
or  cooling.   This  method  will  produce  diagrams  liice  those  shown 
in  Figure  2,  on  page  573. 

If  a  body  undergoes  an  abrupt  change  in  physical  properties 


Civil  Engr-8  B-          Assignment  21.  page  5. 

(as  -when  it  melts  or  vapor izes),  a  quantity  of  heat  is  aosorbed 
or  given  off  without  changing  the  temperature  of  the  body.  The 
heat  absorbed  during  the  change  in  state  of  a  body  is  called 
latent  heat.   Latent  heats  will  have  a  marked  affect  on  the  cool- 
ing curves.   If  all  the  heat  given  off  by  a  body  is  furnished  at 
the  expense  of  the  temperature  of  the  body,  that  is,  if  it  dis- 
appears as  sensible  heat,  the  cooling  curve  will  be  smooth  and 
continuous  as  (a),  in  Figure  2,  on  page  573.  Horizontal  portions 
or  arrests  in  the  cooling  curve  indicate  that  the  temperature  is 
maintained  by  the  evolution  of  a  certain  amount  of  latent  heat. 
See  (b)  in  Figure  2.   The  curve  belo\v  the  freezing  point  or 
arrest  in  the  cooling  is  similar  to  that  in  Diagram  (a).  The 
cooling  curve  for  water  should  be  familiar,  since  it  falls  -within 
ordinary  experience.  When  water  is  subjected  to  a  low  temperature 
it  will  lose  heat  steadily  until  the  freezing  point  is  reached 
at  zero  degrees  Centigrade.  At  this  point  the  -water  will  continue 
to  lose  or  radiate  heat,  but  its  temperature  will  remain  at  zero 
until  all  the  water  is  changed  into  ice.  During  this  second 
period  radiated  heat  is  given  off  at  the  expense  of  the  so-called 
latent  heat  of  fusion  of  ice.   Further  radiation  is  at  the  expense 
of  sensible  heat  and  the  temperature  of  the  ice  falls  until  it 
becomes  that  of  the  surrounding  medium.   The  cooling  curve  of 
liquid  antimony  or  any  pure  metal  near  its  solidification  point 
is  very  similar  to  the  cooling  curve  of  water.   The  curve  is 
similar  to  that  in  diagram  (b)  in  Figure  2. 


Civil  Engr-8  B- 


Assignment  21. 


Page  6 


Study  Article  625  on  cooling  curves.  Temperature  -  time 
diagrams  such  as  are  shown  in  Figure  2  are  not  well  adapted  to 
show  small  evolutions  o*  heat  in  an  alloy  such  as  steel.  An 
inverse  rate  curve,  however,  will  magnify  the  changes  in  direction 
of  the  cooling  curve  and  permit  a  more  accurate  determination  of 
critical  temperatures.  The  data  for  an  inverse-rate  curve  are 
obtained  by  reading  and  recording  the  time  required  for  the  body 
to  cool  through  equal  intervals  of  temperature.  The  following  is 
an  inverse-rate  cooling  curve  for  0.4$  carbon  steel ; 


1 
t+ 

I 

CD 
6-1 


Time   Intervals 
Figure     1. 

The   equilibrium  diagram  for  alloys   of  carbon  and   iron  is 
obtained   from  inverse-rate   cooling  curves  for   a  complete   series   of 
alloys.     The   critical  points  are  more   readily  determined   from 
these  diagrams  tha&  from  the   ordinary  cooling  curve.     An  ordinary 
cooling  curve  for  0.4%     carbon  steel   is  as  follows: 


Civil  Engr-8  B. 


Assignment  21, 


Page  7 


Time 
Figure  2 

The  critical  points  are  scarcely  perceptiole,  and  if  the  curve 
were  dra?/n  from  experimental  points,  the  breaks  or  arrests  in  the 
curve  would  be  determined  only  with  difficulty.  The  superiority 
of  the  inverse -rate  curve  is  evident. 

An  equilibrium  diagram  is  shown  on  page  591.   It  is  of 
great  importance  in  the  study  of  iron  and  steel.   Other  names 
for  this  diagram  are  given  in  Article  626:p  about  the  middle  of 
page  574.  Equilibrium  diagram  is  as  good  a  name  as  any  of  those 
listed. 

Study  Articles  627  to  630.   The  freezing  of  binary  alloys 
which  solidify  by  selective  freezing  is  fully  explained  in  these 
articles.  The  constituents  in  this  type  of  alloy  separate  in 
freezing.   Lead  and  tin  form  such  an  alloy.  An  equilibrium 
diagram  for  water  and  salt  is  like  that  shown  on  page  575.  That 
part  of  the  iron-carbon  equilibrium  diagram  (shown  on  page  591) 
to  the  right  of  the  2%  carbon  line  is  analagous  to  that  of  the 
binary  alloys  in  which  the  state  of  solution  is  not  maintained  in 


Civil  Engr-8  B.          Assignment  21.  Page  8. 

the  solid  state,  namely  to  those  -which  solidify  by  selective 
freezing.   Primary  austenite  which  will  be  described  later,  in- 
stead of  iron,  separates  from  the  melt  to  the  left  of  the 
eutectic  point. 

The  temperature  at  which  an  alloy  of  this  type  begins  to 
solidify  depends  upon  the  relative  percentages  of  the  constitu- 
ents.  If  this  is,  say,  the  point  X,  in  the  diagram  in  Figure  3, 
freezing  v/ill  begin  at  temperature  j.   Remember  that  only  the 
melt  or  mother  liquor  is  enriched  in  constituent  B ,  since  crystals 
of  W  separate  out  of  the  solution.   The  composition  of  the  alloy 
always  remains  as  represented  by  the  percentages  at  the  point  X. 
Note  that  the  cooling  curve  for  an  alloy  of  the  composition  X  is 
represented  in  Figure  2,  diagram  (d),  on  page  573. 

The  term  eutectic  is  used  for  the  first  time  in  this 
article.   It  is  taken  from  a  combination  of  the  two  Greek  words 
which  mean  "well"  and  "melting".  The  meaning  of  the  term  eutectic 
is  taken  as  easily-melted ,  or  literally,  low-melting.  A  mother 
liquor  which  always  has  the  same  composition  for  given  constituents, 
and  a-ioonstant  freezing  point,  and  which  remains  liquid  longest, 
or  in  other  -words  which  has  the  lowest  melting  point,  is  called 
the  eutectic  of  the  given  constituents.  The  fact  that  a  eutectic 
has  a  constant  melting  point  and  hence  a  constant  composition 
led  early  investigators  to  believe  that  it  was  a  chemical  com- 
pound,.  Later  it  was  shown  that  its  constituents  were  not  in  any 
simple  molecular  ratio.   Furthermore  microscopic  examinations  of 


•• '  •' '  :.. 

, 


.  Civil  Engr-8  B.         Assignment  21.  Page  9. 

eutectics  (see  the  illustrations  on  page  597),  showed  that  they 
are  not  homogeneous  substances,  but  a  mechanical  mixture  of 
minute  cyrstal  grains  of  the  const ituents. 

Study  Articles  631,  632,  and  633  on  the  binary  alloys  in 
which  the  constituents  in  solution  in  the  liquid  remain  in  solu- 
tion in  the  solid  state;  in  other  words  those  in  v?hich  they  form 
a  solid  solution.  The  diagram  in  Figure  8  on  page  579  illustrates 
the  binary  character  of  the  gold-silver  alloys,  which  are  of  this 
type.  The  regions  II  and  IV  to  the  left  of  the  2$£  carbon  content 
as  indicated  by  the  point  S  in  the  iron-carbon  equilibrium  diagram 
in  Figure  1,  on  page  591,  is  a  region  of  non-elective  freezing  and 
shows  a  situation  analagous  to  the  freezing  of  the  alloys  discussed 
in  this  article. 

Study  Articles  634,  635,  and  636.  These  articles,  together 
with  similar  ones  previously  studied,  form  the  basis  for  a  study  of 
the  iron-carbon  equilibrium  diagram  which  is  of  importance.  The 
area  of  this  diagram  to  the  left  of  the  2%  carbon  content  line 
shows  selective  freezing  from  a  solid  solution  with  the  formation 
of  a  eutectic.  To  differentiate  this  latter  eutectic  from  the 
one  at  point  E  in  the  diagram  on  page  591,  which  is  a  true  eutectic., 
since  it  is  formed  from  a  mother  liquor  or  solution,  it  is  given 
the  nane  sutectoid ,  a  term  which  is  interpreted  as  meaning  "some- 
thing  of  the  nature  of  a  eutectic". 

Be  able  to  draw  characteristic  equilibrium  diagrams  and  ex- 
plain the  process  by  which  freezing  takes  place. 


Civil  Fngr-8  B.          Assignment  21.  Page  10. 

The  discussion  of  alloys  of  more  than  two  components  need 
not  be  studied.   It  would  "be  of  use  in  the  discussion  of  alloy 
steels  "but  in  this  text  they  are  not  treated  in  much  detail. 

The  information  in  this  assignment  is  rather  different 
from  that  in  any  so  far  studied.  The  student  should  put  forth  an 
effort  to  master  the  fundamental  principles  discussed  in  the  text. 
No  thorough  discussion  of  iron  and  steel  can  be  made  without  use 
of  the  equilibrium  diagram  and  before  it  can  be  used  with  facility 
the  fundamentals  given  in  Chapter  XX  in  the  text  must  be  understood. 


Civil  Engr-8  B .  Assignment  21.  page   11. 

QUESTIONS 

1.  How  does  a  mixture  differ  from  a  solution?  From  a  compound? 

2.  What  is  a  solid  solution? 

3.  What  is  a  eutectic? 

4.  What  is  a  eutectoid? 

5.  Define  allotropy.  What  is  its  relation  to  the  study  of 

iron  and  steel? 

6.  Draw  a  cooling  curve  for  water  near  its  freezing  point. 

7.  What  is  an  inverse -rate  curve?  What  is  it  used  for? 

8.  Explain  the  reason  for  the  horizontal  parts  or  arrests  in 

a  normal  cooling  curve- 

9.  Would  you  expect  to  find  perfectly  shaped  crystals  in 

commercial  steel?  Why? 

10.  Draw  an  equilibrium  diagram  for  a  "binary  alloy  and  explain 

hovr  it  freezes  if  the  state  of  solution  is  not  maintained 
in  the  solid  state. 

11.  Why  are  metals  alloyed? 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 
Civil  Engr-3  B.  Professor  C.T.  Wiskooil 

Assignment  22. 
THE  CONSTITUTION  OF  IRON  AND  STEEL 

The  necessity  for  alloying  pure  iron  is  briefly  stated  in 
Article  639.  The  reasons  for  alloying  metals  in  general  were 
given  at  the  "beginning  of  the  previous  assignment  on  the  "Forma- 
tion and  Structure  of  Alloys".   In  this  discussion,  pure  steel 
will  be  considered  as  an  alloy  of  iron  and  carbon.   In  ordinary 
steels  there  are,  besides  these  elements,  sulphur,  manganese, 
phosphorus,  oxygen,  and  silicon,  together  with  traces  of  copper, 
aluminum,  and  nitrogen.  Carbon  and  other  elements  added  purposely 
are  essential  ingredients;  the  others  are  impurities.  The  marked 
effect  that  additions  of  carbon  to  pure  iron  have  on  the  result- 
ant alloy  are  due  to  the  changes  caused  in  the  structure.  This  is 
very  evident  from  microscopic  studies  of  these  alloys.  See  the 
illustrations  on  page  596  >  Because  of  the  effect  carbon  has  on 
the  physical  and  mechanical  properties  of  steel,  its  presence  is 
necessary  in  very  small  amounts  only.  Even  in  the  hardest  tool 
steels  it  does  not  exceed  1.5$  by  weight.   Carbon  is  usually 
measured  in  hundredths  of  one  per  cent,  each  unit  (or  1/100  of  one 
percent)  of  which  is  spoken  of  as  a  point.  A  steel  having  a 
carbon  content  of  0.25$  would  be  designated  as  25-point  carbon 
steel. 


Civil  Engr-8  B- 


Assignment  22. 


Page  2, 


Steel  was  defined  in  Assignment  19  under  the  subject 
Manufacture  of  Steel.   You  should  be  able  to  give  definitions  in 
Articles  640  to  655  at  the  time  the  materials  in  question  are  dis- 
cussed and  should  make  no  attempt  to  remember  definitions  of 
materials  that  are  not  discussed*  Furthermore,  you  should  not 
memorize  definitions  in  the  words  of  the  text,  but  should  define 
materials  and  processes  in  your  own  words.  Read  over  Articles 
640  to  655  inclusive  and  see  hovr  your  own  definitions  agree  with 
those  in  the  text. 

Read  Article  656  but  omit  the  table.   The  equilibrium 
diagram  for  alloys  of  iron  and  carbon  will  now  be  taken  up  in  de- 
tail.  The  remainder  of  the  chapter  should  be  carefully  studied. 

The  critical  temperatures  for  pure  iron  are  given  in 
Article  658.  Critical  temperatures  were  referrecd  to  in  the  previ- 
ous assignment,  number  19,  under  the  discussion  of  cooling  curves. 
If  eutectoid  steel  is  considered  it  will  be  found  to  have  only  one 
critical  point.   The  heating  and  cooling  curve  would  be  approximate' 
ly  as  f  ollov/s  : 


^ecalescence 

Point 


r— Removed  from  furnace 

Recalescence  Point 


Cooling 


Time 


Civil  Bngr-8  B-          Assignment  22,  Page  3. 

As  explained  in  the  text  the  critical  points 'are  higher  on  heating 
than  on  cooling.   The  recalescence  point  for  eutectoid  steel 
(0. $%  car"bon)  is  about  690  degrees  Centigrade,  Since  the  structur- 
al changes  -which  occur  do  not  take  place  suddenly  the  critical 
temperature  or  critical  point  is  more  properly  designated  by  the 
term  critical  range,   "When  eutectoid  steel  passes  through  its 
critical  range  during  the  process  of  cooling  the  temperature  of 
the  steel  will  actually  rise  if  the  conditions  are  favorable.  An 
attempt  has  been  made  to  show  this  condition  in  the  diagram  just 
given.   In  the  case  of  pure  iron  the  change  in  rate  of  cooling  is 
not  very  marked.  There  is  no  actual  rise  in  temperature ,  or 
recalescence,  at  the  critical  temperature  which  occurs  about  900° 
Centigrade   The  leaver  critical  range  at  760°C.   is  less  marked 
than  the  first.  Below  760°  the  steel  cools  normally  to  atmospheric 
temperatures.   In  a  lor;  carbon  steel,  say  one  having  0.1$  carbon, 
there  are  three  thefVftl  retardations..  The  most  pronounced  is  at 
850°  c,  the  second  about  760°  and  the  third  near  700°c  The  last 
tvro  are  quite  indistinct.  As  carbon  is  added  to  the  alloy  the  two 
upper  critical  temperatures,  found  in  the  10-point  carbon  steel, 
will  approach  each  other  and  at  carbon  contents  of  .35  to  .4C$  will 
merge  into  one,  so  that  these  steels  have  only  two  critical  tempera- 
tures, one  at  about  740°   and  the  other  at  about  700°.  Further 

f\ 

additions  of  carbon  seera  to  cause  the  t7/o  remaining  critical  tem- 
peratures to  merge  into  one  at  about  C.6^  carbon  and  over-  Theoreti- 
cally the  merging  should  not  occur  until  the  eutectoid  composition 
is  reached  at  O.S?£  carbon,   The  actual  determination  of  two  critical 


Civil  Engr-3  B.          Assignment  22,  Page  4. 

temperatures,  -when  they  are  close  together,  is  very  difficult,  and 
this  fact  accounts  for  the  apparent  merging  with  the  lesser  per- 
centage  of  carbon . 

The  critical  ranges  are  illustrated  in  the  equilibrium 
diagram.  The  diagram  on  page  591  refers  to  the  critical  ranges 
on  cooling.  All  critical  ranges  are  denoted  "by  the  letter  A. 
TO  indicate  the  period  of  heating  the  A  is  followed  by  a  small 
c,  which  stands  for  the  French  word  "chauffage"  which  means 
heatingo  Ar  denotes  a  critical  temperature  on  cooling,  the  r 
being  the  abbreviation  for  the  word  "refroidissement" ,  meaning 
cooling.  The  designation  Ac  and  Ar  are  further  modified  by 
the  numerals  1,  2  and  3  to  signify  the  critical  ranges  in  the 
order  they  are  encountered;  thus,  Acj  means  the  first  critical  ra 
range  encountered  upon  heating  the  steel. 

In  carbon  steels  there  is  a  difference  of  about  30  degrees 
between  the  critical  temperature  on  heating  and  the  critical 
temperature  on  cooling..  Theoretically  these  temperatures  should 

be  the  same.   It  lias  been  proved  that  one  important  factor  caus- 

teiaperature 
ing  this/lag  is  the  ordinary  phenomenon  of  hysteresis*  The  process 

of  slow  heating  and  cooling  bring  these  critical  temperatures 
closer  together.  Two  other  minor  causes  for  the  difference  are 
the  impurities  contained  in  the  steel    The  maximum  temperature 
to  which  the  steel  is  heated  is  another  factor  which  causes  a 
temperature  lag  between  the  critical  points.  For  ordinary  com- 
mercial steels  and  usual  practice  these  latter  causes  are  of  no 
consequence. 


Civil  Engr-8  B.  Assignment  22.  Page  5. 

Cementite  and   ferrite,     two  important  constituents   of  steel, 
are  lefined   in  Article  659.     Ferrite   is   soft,  weak,  and  ductile. 
Its  tensile   strength  is  estimated  to  "be  about  40,000  lb,   per   sq. 
in.      It   is  strongly  magnetic  and  has  a  high  electric  conductivity* 
It  has  no  hardening  poorer  *     Ferrite  appears  "best  in  microphoto- 
graphs  of  low  carbon  steel,   containing  from  10  to  30-point  of 
carbon;     in  these  raicrophotographs   it  has  a  white  color.,      See 
(b),    (c),   and   (d)   in  Figure  3  on  page  596. 

When  steels  are  cooled  from  a  high  temperature  all  the 
carbon  is  combined  with  iron  in  a  chemical  compound  ^nich  in 
microphotographs  is  alyrays  referred  to  as  cementrte.     Steel  made 
by  the  cementation  process  contains  considerable  cementite 
(Fe-zC)       Little   is  known  of  its  actual     properties  except  that 
it   is  the  hardest  constituent  of  steel.      It  will  scratch  glass 
but  not  quartz .      It   is  very  brittle.     Cementite   is  thought  to 
have  a  high  shearing  strength  but  to  be  weak  in  tension.      It 
occurs  free   in  hypereutectoid   steels;     see    (g)   and   (h)    in  Figure 
3   on  page  596. 

Pearlite   is  defined   in  the  first  paragraph  on  page  592. 
The  eutectoid  of  steel  is  called  pearlite  because   of  its  resenfa 
b lance  to  mother   of  pearl*      It   is  a  mechanical  mixture   of  minute 
crystals   of  cementite  and  ferrite.   always   in  definite  proportions 
as  given  in  the  text.      It  contains  approximately  0,9$     carbono 
Pearlite  commonly  occurs   in  slowly  cooled   steels   in  the   lamellar 
phase  which  is  shown  in  (b)   of  Figure  4  on  page  597,    in  which 


Civil  Engr-8  B.          Assignment  22.  Page  6. 

it  is  composed  of  alternate  layers  of  ferrite  and  cementite.  Note 
the  high  magnification  necessary  to  bring  out  the  required  detail 
in  the  illustration  referred  to.  Besides  existing  in  globular 
form," ras  shown  in  (a)  of  the  same  figure,  pearlite  has  been  found 
to  exist  in  three  other,  but  less  important,  forms.  The  size  of 
the  grains  has  a  marked  effect  on  the  strength  of  pearlite.  Under 
normal  conditions  its  maximum  tensile  strength  is  estimated  to  be 
over  100,000  Ib.  per  sq»  in.    It  is  about  2.5  times  harder  than 
ferrite,  but  it  is  not  hard  enough  to  make  tools  which  require  a 
cutting  edge. 

Austenite  (named  after  Sir  Roberts -Austen)  is  a  substance 
determined  microscopically  as  a  constituent  of  steel  under  certain 
conditions  and  regarded  as  a  solid  solution  of  carbon  or  iron 
carbide  in  iron.  See  paragraph  IV  on  page  591  in  the  text. 

Be  able  to  draw  the  iron-carbon  equilibrium  diagram  given 
on  page  591.   Include  in  this  diagram  as  much  information  as 
possible.   In  the  construction  it  is  necessary  to  remember  the 
location  of  certain  important  points,  such  as  A,  G,  0,  P,  S, 
and  E.  When  these  points  are  located  the  main  lines  in  the  diagram 
can  be  sketched  in.  The  eutectic  contains  about  4.3$  carbon. 
This  is  point  E  in  the  diagram.   For  hyper-eutectic  alloys 
graphite  separates  from  the  melt  along  ED  until  the  point  E  is 
reached,  when  the  eutectic  solidifies*   It  might  be  expected  that 
iron  would  separate  from  the  melt  along  the  line  jffi.  This,  how- 
ever, is  not  the  case,  but  a  mixture  of  iron  and  carbon  contain- 
ing approximately  2%  carbon  and  knovm  as  primary  austenite  sepav- 


Civil  Engr-8  Bo          Assignment  22.  Page  7. 

rates  from  the  melt  to  the  right  of  the  point  S  in  the  diagram. 
In  this  portion  of  region  II  the  iron-carbon  alloys  exhibit  the 
phenomenon  of  selective  freezing,  as  do  the  lead-tin  alloys-  See 
Figure  3  on  page  575.  To  the  left  of  point  S,  or  in  alloys 
having  less  than  2$  carbon,  the  freezing  is  non-selective,  simi- 
lar to  that  of  the  alloy  whose  equilibrium  diagram  is  shovm  on 
page  579*  This  kind  of  freezing  is  characteristic  of  the  gold- 
silver  alloys.     Consider  an  iron-carbon  alloy  having  about 
1.5%  carbon  at  a  temperature  of  1500°  C°   It  is  a  solution  of 
carbon  in  iron,  which  if  allowed  to  cool  will  begin  to  crystallize 
trhen  the  temperature  reaches  the  line  AE  or  about  1400°  C-  Solidi- 
fication will  continue  until  the  temperature  reaches  a  point  on 
the  line  AS,  or  about  1220°  C,  at  which  point  the  solution  is  ex- 
hausted and  the  entire  mass  becomes  solid.  Each  crystal  that 
separates  from  the  me It  will  contain  1.5$  carbon;  therefore,  the 
entire  mass  is  a  solid  solution  of  carbon  and  iron.   It  is  also 
known  as  primary  austenite. 

During  the  cooling  of  primary  austenite  ih  the  region  IV, 
below  the  line  AS,  it  undergoes  changes  similar  to  tlt&ps&t  which 
occur  the  cooling  of  a  liquid  solution.  Along  the  line  PS,  for 
alloys  having  more  than  .9$  carbon  and  known  as  hyper-autectoid 
steels,  cement ite  is  precipitated .  For  alloys  having  less  than 
•9$  carbon,  that  is  hypo-eutectoid  steels,  pure  iron  or  f err ite 
is  thrown  out  along  the  line  GOP  until  the  eutectoid  composition 
is  reached.  At  this  point  both  f err ite  and  cement ite  are  precipi- 


Civil  Engr-f8  B-         Assignment  22.  page  8. 

tated  at  the  same  time  and  the  eutectoid  pear  lite  is  formed.  The 
change  from  austenite  to  pearlite  is  not  instantaneous;  "but,  as 
irill  be  explained  under  the  discussion  of  heat  treatment  and 
tempering,  the  austenite  may  pass  through  a  series  of  stages  in 
•which  it  is  known  as  martensite,  troostite,  and  sorbite;  finally 
it  becomes  pearlite.   If  a  steel  which  contains  0. 9j£  carbon  is 
cooled  slowly  from  a  point  above  its  critical  temperature,  so  that 
it  will  have  an  opportunity  to  pass  through  all   transition 
stages,  it  will  consist  entirely  of  pearlite  and  be  known  as   a 
eutectoid  steel. 

Steel  having  above  0.3$  carbon  is  supposed  to  have  the 
ability  to  harden  but  edge  tools  are  usually  made  from  low  carbon 
steels,  in  which  the  carbon  ranging  froa  50  to  125  point.  While 
2.Q;^is  the  theoretic  division  line  between  steel  and  cast  iron, 
coiimercial  tool  steels  rarely  exceed  150  point  carbon  (1.5$ 
carbon).  Commercial  cast  irons  usually  range  between  2.2  and 
4«0j£  carbon- 

Most  of  the  information  discussed  in  connection  with  the 
iron-carbon  equilibrium  diagram  is  given  in-  the  following  sketch: 


Civil  Engineering-SB 


Assignment  22 


Page   9 


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Civil  Engr-8  Bo  Assignment  22.  Page   10« 

QUESTIONS 

le  What  is  meant  "by  the  critical  temperature  of  steel? 

2.  Define  the  term  "recalescence  point"  as  applied  to  steel. 

3.  Why  are  the  critical  temperatures  higher  when  steel  is 
"being  heated  than  when  it  is  "being  cooled? 

4.  What  is  ferrite?  What  are  some  of  its  properties? 

5.  What  is  cementite?  Write  its  formulae 

6.  What  is  austenite? 

7.  What  is  pear lite?  In  what  forms  does  it  usually  exist? 
8»  What  is  hyper-eutectoid  steel? 

9c  What  is  the  usual  range  in  carbon  content  for  steels  used  in 
the  manufacture  of  edge  tools? 

10-  Draw  a  carbon- iron  equilibrium  diagram.  Uark  all  important 
points  ancl  areas.  It  is  important  that  the  temperatures 
and  carbon  contents  be  indicated  on  the  diagram. 


UNIVERSITY  OF  C AL IF ORFIA  EXTENSION  DIVISION 

Correspondence  Courses  • 
Materials  of  Engineering  Construction 

Assignment  23. 
Civil  Fngr-8  B.  Professor  C-T-  Wiskocil 

PROPERTIES  OF  WROUGHT  IRON 

Structure  ;-  Read  Article  664-  The  structure  of  wrought 
iron  is  clearly  shown  in  Figure  1  on  page  598.  The  greater  part 

of  wrought  iron  is  pure  ferrite;  in  fact,  this  material  approaches 

:ahy/ 
nearer  to  pure  iron  than  /.other  coonercial  form  of  iron.   In 

both  the  transverse  and  longitudinal  sections  the  characteristic 
slag  inclusions  can  "be  seen.   In  the  longitudinal  section,  the 
slag  follows  the  direction  of  rolling  in  dark  lines  of  varying 
thickness;  and  in  the  transverse  section  it  appears  as  irregular 
dark  areas.  An  examination  of  the  structure  of  wrought  iron,  which 
can  "be  made  in  several  ways,  is  the  only  positive  method  of  dis- 
tinguishing this  icaterial  from  low  carbon  steel.   In  the  •wrought 
iron  a  snail  amount  of  carbon  is  always  present  and  this  combines 
with  the  ferrite  to  form  cenentite.   The  cernentite  is  present  in 
such  small  quantities  that  none  remains  in  the  free  state;   it  is, 
however,  present  in  the  form  of  pear lite.  .The  pearlite  is  not 
conspicuous  but  is  distributed  in  small  isolated  areas  between  the 
grains  of  ferrite »  Normal  wrought  iron  contains  about  2.5%  slag, 
96 . 5$  iron,  and  the  remaining  l*v$  silicon,  phosphorus,  sulphur, 
carbon  and  manganese. 

"When  wrought  iron  is  tested  in  tension,  the  fracture  reveals 
a  fibrous  structure.  As  explained  in  this  article  the  fracture  of 


Civil  Engr-8  B.  Assignment  23.  Page  2. 

•wrought  iron  which  is   impure  or  adulterated   (with  steel  scrap)  may 
have  a  crystalline  appearance.     This  type   of  fracture  may  occur, 
too,  when  the   load   is   suddenly  applied   so  that  the   fibers  do  not 
have  time  to  drav:  out  as  under  conditions   of  the  normal  tensile 
test. 

Defects ;-      Read  Article  665°       Since  the   impurities  usually 
combine  with  the  slag  they  are  not  as  important  as  in  the  case  of 
steelc     Sulphur  and  phosphorus  are  the  principal  impurities* 

Tens i le  strength : -         Read  Articles  666  and  667.     As  would 
"be  expected,  the  tensile  strength  of  wrought  iron  depends  upon  the 
relation  between  the  direction  of  the  fibers   (which  in  turn  depends 
upon  the  direction  of  rolling)  and  the  direction  of  the  applied 
stress.     Even  when  the  tensile  stress  is  parallel  with  the  fibers 
the  strength  of  wrought  iron  is  quite  variable .     An  average  value 
may  be  taken  as  50 .,000  Ib.    per  sq.    in.   ultimate,  with  a  proportional 
limit   of  about  30,000  Ib.    per  sq.    in.     The   strength  when  stressed 
norral  to  the  direction  of  rolling,  as  may  occur   in  plates,  may 
be  taken  as  3/4     of  the  values  given  for  the  strength  parallel 
with  the  fibers. 

The  ductility  is  also  quite  variable.  The  average  may 
be  taken  as  35  %,  measured  in  terms  of  the  elongation  in  a  2-inch 
gage  length. 

The   stress-deformation  curves  resemble  those  for  mild  steel. 

Tensile  strength  across  the  grain;-       Read  Article  667. 
As  already  stated  this  may  be  taken  as  75  %     of  the   strength 
parallel  with  the  grain*     The  text  gives  more  detailed   information 


Civil  Engr-8  B  Assignment  23.  page  3o 

on 'wrought  iron  than  is  warranted  "by  its   importance . 

Corxpressive  strength:-     Read  Article  668°     The  ultimate 
strength  of  ductile  materials  like  wrought   iron  is  taken  as  the 
proportional  limit  strength;       30,000  Ib*   per   sq*    ine 

Shearing  strength:-       Read  Article  669 *      If  wrought  iron 
re re   one   of  the   important   structural  materials   it  would  be  necessary 
to  remember  the  details  of  information  such  as  are  given  in  this 
article.      Since   it  is  not,    it  is  sufficient  to  note  that  the 
shearing  strength  is  about  the  same     as  the  tensile  strength., 
30,000  Ib.   per  sqn    in.,  and  that   it  varies  in  a  manner  similar 
to  that  exhibited  by  the  tensile   strength. 

Modulus  of  elasticity:-         Read  Article  670.     Take  the 
average  modulus  of  elasticity  as  27,000,000  Ib.   per  sq.    in* 

Effects   of  overstrain;   -      Read  Article  671.     Overstrain 
is  produced  by  cold  working,   such  as  rolling,  hammering  and 
pressing  at  a  temperature  below  690°  C-      In  general  the  effect  of 
overstrain  is  to  raise  the  ultimate        strength  and  decrease  the 
ductility. 

Toughness  of  wrought   iron;-     Read  Article  672.     Toughness 
is  determined  by  the   impact  test.     The  toughness   of  wrought   iron 
and  mild   steel  are  about  the   same;  no  quantitative  value   is 
assigned* 

Wrought   iron  chains—       Read  Article  S73.     The  strength  of 
wrought  iron  chains  may  be  taken  as   1.6  that  of  the  material 
from  which  the  links  are  made* 


Civil  Engr-8  Be          Assignment  23?  page  4. 

The  welding  of  wrought  iron-   Read  Article  674.   One  of 
the  most  important  properties  of  wrought  iron  is  the  ease  with 
i7hich.it  can  "be  welded.   Low  carbon  steel,  when  the  impurities  are 
lor;,  can  "be  welded  quite  as  easily  as  wrought  iron,  but  other 
steels  are  not  so  readily  welded.  The  welding  temperature  is 
close  to  the  melting  point,  at  which  point  or  range  in  temperature 
the  iron  is  very  plastic.  But  at  this  high  temperature  two  con- 
ditions arise  which  affect  the  weld.  One  affects  the  operation  of 
v/elding  while  the  other  affects  the  strength  of  the  weld»   In  the 
first  case,  the  oxygen  in  the  air  combines  readily  with  the  iron 
at  ITS Id ing  temperatures  and  the  coating  of  iron  oxide  which  forms 
on  the  surface  prevents  a  perfect  union  of  the  parts  of  the  weld. 
In  the  second  case,  welding  temperatures  also  cause  a  coarse 
crystalline  structure  which  decreases  the  strength  of  the  metal  and 
increases  its  brittleness. 

The  oxide  or  slag  which  forms  on  the  metal  is  forced  out  of 
the  weld  when  the  surfaces  are  made  convex,  as  indicated  in  Figure 
8  on  page  607.   The  parts  come  into  contact  at  the  center  and  as 
the  joint  is  hammered  or  forged,  the  slag  is  squeezed  out.  This 
action  is  facilitated  by  the  use  of  a  flux  such  as  borax  which 
makes  the  slag  more  liquicu  Sand  is  used  as  a  flux  in  welding  steel, 

Coarse  crystallization  can  be  prevented  by  working  the' 
metal  until  it  has  cooled  through  its  critical  range  in  temperature . 
The  metal  just  at  the  weld  is  usually  thoroughly  worked  by  hammer- 
ing so  that  the  welds  as  a  rule  do  not  break  at  the  joint  but  some 


Civil  Engr-8  B.          Assignment  23=  page  5 . 

distance  "back.  As  welding  is  usually  done  the  pieces  are  only 
slightly  scarfed  and  the  joint  only  is  hammered.   If  a  bar  welded 
in  this  manner  is  "bent,  it  will  usually  break  just  outside  the 
weld.  Blacksmiths  often  assert  that  the  weld  is  stronger  than  the 
bar.  The  weakness  in  the  bar,  however,  has  been  developed  by  the 
method  of  welding.   If  the  ends  of  the  bar  to  be  welded  are  first 
heated  to  a  moderate  welding  temperature  and  stove  up  (hammered 
on  the  ends  to  make  the  section  thicker)  and  if  a  well  beveled 
scarf  is  made,  instead  of  the  short,  blunt  one  usually  put  on,  the 
chances  for  a  better  weld  are  much  improved.  The  ends  are  then 
reheated  to  welding  temperature,  the  flux  applied  and  the  weld  made 
in  the  usual  manner.  If  the  ends  have  been  properly  stove  up,  the 
bars  will  have  to  be  hammered  where  the  grain  size  has  been  in- 
creased by  the  high  temperature,  so  that  when  the  joint  is  worked 
dorm  to  size  it  will  have  been  hamnered  well  back  from  the  center  of 
the  weld,  on  account  of  the  long  scarf,  and  no   weak  spots  will 
be  left.  The  bar  trill  then  have  a  uniform  structure  and  should  be 
equally  strong  throughout  its  length.  Electric  heating  is  more 
efficient  than  forge  heating  and  power  fudging  produces  a  better 
weld  than  hand  methods. 

Methods  of  distinguishing  wrought  iron  from  soft  steel ;- 
Read  Article  675.  Methods  for  distinguishing  wrought  iron  from 
steel  have  been  discussed  in  Assignment  No*  19.   It  is  proper  to 
emphasize  at  this  time  that  the  only  positive  method  of  identifying 
wrought  iron  is  by  an  examination  of  its  structure.  This  can  be 


.  •  '-  *• 


Civil  Engr-3  B.  Assignment  23.  page  6- 

made  "by  methods  suggested   in  this  article   or  "by  the  regular  micro- 
scopic methods.. 

PROPERTIES  OF  STEEL 

The  principal  factors  which  influence  the  properties  of 
steel:-         Read     Article  676*     The  quality  and  mechanical  prop- 
erties      of  steel  are  affected  "by   (a)     the  method   of  manufacture, 
(b)     the  composition,    (c)  mechanical  TTorlc,  and   (d)  the  heat 
treatment,,      It  must  "be  remembered  that  while  these  factors  are 
discussed   separately,  all  of  them  may  have  an  effect  on  the 
quality  and  properties   of  a  given  piece   of  steel. 

Effect  of  carbon:-       Read  Articles  677  to  685  inclusive* 
This  element  is  employed  as  the  controlling  constituent  in  reguia 
lating     the  properties  of  common  steels    (so  called   straight 
carbon  steels).     The  effect   it  has   on  the  mechanical  properties 
is  discussed  in  detail  in  the  text.      Its  most  important  influence 
is   on  the   strength,  hardness  and  ductility  of  the  metal.       Heat 
treatment,  which  Trill  be  discussed  separately,   has  a  marked  effect 
on     carbon  steels.     Beginning  with  pure   iron  which  is  soft  and 
ductile,  additions   of  carbon  to  normally  cooled  steel  increase 
the  hardness  and   strength  and  decrease  the  ductility,  until 
eutectoid  composition     (0.9  %  carbon)    is  reached.     For  each  10 
points   (1/10  of  one  par  cent)   of  carbon  added,,  the  yield  point 
is  raised  about  3,990  Ib.    per  sq.    in* ,   the  maximum  tensile 
strength  is  increased  about  9,360  lb.   per   sq.    in.,   and  the  per- 


Civil  Engr-8  B .  Assignment  25»  Page  1, 

centage  elongation  is  reduced  about  4.3  f**     Above  this  point 
further  additions  of  carbon  result  in  increasing  hardness  and 
strength  but  more  rapidly     decrease  the  brittleness«     The  use   of 
high  carbon  steel  is  restricted  to  products  in  which  great  hard- 
ness  is  the  principal  requirement  and  toughness  and  ductility  are 
not  so  necessary.     Commercial  steels  rarely  exceed   1.20  %  carbon. 
Straight  carbon  steels  most  generally'  usfful  in  the  hardened 

state  have  carbon  contents  ranging  from  .9  to  1.2  %\     they  are 
sufficiently  hard  for  most  uses  and  yet  are  not  brittle  to  an 
objectional  degree. 

The  general  shapes  of  stress-deformation  curves  as  influence 
ed  by  the  carbon  content  are  given  on  pages  611  and  612.     Note 
that  the   slope   of  the  curve,  which  determines  the  modulus  of 

elasticity,    is  not  affected  by  changes  in  the  carbon  content. 

the   statements   in 
The  results  shown  agree  v/itly Article  681,       The     average  value 

for  the  modulus   of  elasticity  may  be  taken  as  30,000,000  Ib.   per 
sq.    in.    for  all  steels  and  for  both  tension  and  compression. 
Average  figures  should  be  remembered.     Take   ordinary 
structural  steel   (rolled  inild  carbon,  steel)  which  has  an  average 
carbon  content  of  approximately  0.2  $.      Its  proportional  limit 
is  30,000  Ib.    per  sq<    in.   and   its  ultimate  tensile  strength  is 
60,000  Ib.    per  sq.    in.     The  compressive   strength  may  be  taken  as 
the  proportional  limit,  which  is  the  same   in  tension  and   in 
compression,   30,000  Ib.   per  sq-    in.      Its  ductility  as  measured  by 
the  elongation  is  about  35  j£. 


Civil  Engr-8  B.  Assignment  23.  Page  8. 

Read  Article  683  carefully.   It  explains  why  it  is  imposs- 
ible to  determine  a  yield  point  in  high  carbon  steels.  The  drop- 
of -the -"beam  is  veil  adapted  to  the  determination  of  this  point  in 
the  case  of  Ioi7  carbon  steels.  This  is  also  clearly  shovm  in 
the  diagrams  on  pages  611  and  612  previously  referred  to.   In  the 
strict  interpretation  of  the  term,  high  carbon  steels  do  not  have 
a  yield  point.  The  proportional  limit  can  "be  obtained  only  with 
an  extensometer, 

THE  EFFECT  OF  IMPURITIES 

Read  Articles  686  to  693  inclusive.  A  great  deal  has  been 
•written,  with  considerable  difference  of  opinion,  on  the  effect 
of  various  elements  on  the  properties  of  steel.  I&nganese  -while 
it  is  listed  in  the  text  as  an  impurity,  is  unquestionably 
beneficial.   Oxygen,  7/hich  is  not  mentioned  in  the  text  in  this 
particular  article,  is  decidedly  harmful.  The  effects  of  sulphur 
and  phosphorus  are  considered  to  be  harmful  but  opinion  seems  to 
be  changing  in  this  respect.  Recently  a  committee  organized 
jointly  by  the  A. S.T.L!«  and  the  U«S.  Bureau  of  Standards,  and 
composed  of  representative  engineers  and  investigators  has  been 
studying  the  effect  of  sulphur  and  phosphorus  on  the  properties 
of  rivet  steel. 

Influence  of  oxygen:-  Oxygen  causes  both  red  shortness 
(or  hot -shortness)  and  cold  shortness  in  steel.  The  terms  red-short 
or  hot-short  are  used  to  designate  a  condition  of  brittleness 
in  the  hot  metal.  Cold-shortness  is  the  term  used  to  designate 


Civil  Engr-8  3  Assignment  23v  Page  9, 

brittleness  at  ordinary  temperatures.  These  terns  are  used 
principally  in  connection  with  the  process  rolling*  As  little 
as  .03  %  of  oxygen  produces  brittleness  under  impacts   Large 
amounts  of  oxygen  are  not  necessary  to  produce  harmful  effects^ 
Overblown  Bessener  steel  without  deoxidization  contains  only 
.15$  oxygen,  yet  this  renders  the  netal  unf it  f or  use., 

Influence  of  manganese :~    Read  Article  690=  Manganese 
is  a  powerful  deoxidizing  agent*  That  which  is  left  in  the 
steel  after  deoxidizing  it  causes  it  to  roll  and  forge  better  and 
also  slightly  increaseesthe  tensile  strength  and  hardness..  As 
was  brought  out  in  the  discussion  under  Sulphur,  in  Article  689, 
manganese  conbines  with  sulphur  to  form  manganese  sulphide.. 
For  manganese  to  exert  its  nest  beneficial  effect  it  should  be 
present  in  amounts  greater  than  1.7  times   the  amount  of  sul- 
phur ;  (the  proportion  indicated  in  the  text)   About  five  times 
more  manganese  than  the  amount  of  sulphur  present  should  be  used. 

Influence  of  sulphur ;-   Read  Article  689,   In  the  form 
of  ferrous  sulphide  this  element  will  cause  red-shortness  but  it 
can  be  neutralized  by  manganese  so  that  it  is  comparatively  harm- 
less. The  opinion  has  been  expressed  that  sulphur  up  to  0, 1  % 
does  not  effect  the  strength  and  ductility  of  steel,  The  results 
to  be  published  by  the  A-S't°H<  joint  committee,  previously  re- 
ferred to,  will  be  valuable  since  no  other  thorough  investigation 
has  been  made  on  this  subject.   Specifications  commonly  limit  the 
sulphur  content  to  0.05  %, 


Civil  Engr-8  B.          Assignment  23.  Page  10, 

Influence  of  phosphorus :-   Read  Article  688.  The  con- 
sensus of  opinion  is  that  phosphorus  causes  cold -shortness,  Some 
evidence  has  "been  given  to  prove  that  up  to  0. 1  $  it  does  not 
produce  harmful  brittleness.  This  question  is  also  "being  investi- 
gated by  the  A«.  S-T.M-  Joint  Committee.,   It  is  quite  generally 
agreed  that  additions  of  phosphorus  increase  the  tensile  strength 
and  hardness  and  decrease  the  ductility,  with  an  effect  similar 
to  that  caused  by  the  addition  of  carbon.    ^°r  structural  steels 
most  specifications  limit  phosphorus,  as  they  do  sulphur,  to  about 
0,05 


Civil  Engr-8  B-  Assignment  23.  page   11 

QtJEST  IONS 

1.  Describe  the  normal  structure  of  wrought  iron. 

2.  List  the  ultimate  strength  and  proportional  limit  of  wrought 

iron  in  tension  and  compression;  also  its  modulus  of 
elastic  ity<. 

3.  How  may  wrought  iron  be  distinguished  from  low  carbon  steel? 

4.  Why  is  the  ordinary  weld  weaker  than  the  original  bar? 
SP  What  is  the  proper  method  of  making  a  weld? 

6.  What  are  the  factors  that  influence  the  mechanical  properties 

of  steel? 

7.  Ho?/  does  carbon  affect  the  tensile  strength  and  hardness  of 

steel? 

8.  What  effect  does  carbon  have  on  the  modulus  of  elasticity  of 

steel? 

9.  Explain  why  the  drop-of -the -beam  method  cannot  be  used  to 

determine  the  yield  point  in  the  case  of  high  carbon  steels, 

10.  What  are  the  impurities  in  steel? 

11.  How  does  manganese  effect  the  properties  of  steel? 

12.  What  is  meant  by  hot-  or  red -shortness?  Can  it  be  pre- 

vented ? 

13.  Give  the  approximate  strength  of  ordinary  structural  steel 

in  tension  and  compression.  What  is  its  proportional 
limit?  What  is  its  modulus  of  elasticity?  Give  oiailar 
values  gor  v/r ought  iron. 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 
Civil  Engr  8  B.         Assignment  24.    Professor  C»T.  Wiskccil 


Effects  of  heating  above  the  critical  range:-  Read  Article 


694.   As  will  "be  noted  in  this  article,  there  is  a  change  in  type 
and  size  of  crystals  when  steel  is  heated  above  its  critical  temper- 
ature. When  it  is  heated  through  the  critical  range,  its  pre- 
viously existing  structure  is  obliterated,  or  tends  to  become  ob- 
literated; and  just  above  this  range  in  temperature,  the  steel 
possesses  the  -.'smallest  crystalline  structure  which  it  is  capable 
of  assuming.  The  rate  at  which  the  structure  is  obliterated  de- 
pends upon  the  temperature  reached  and  the  time  the  steel  is 
kept  at  that  temperature.  Simultaneously  with  the  obliteration 
of  the  old  structure  a  new  one  begins  to  grow;  the  size  of 
crystals  increases,  as  a  result  both  of  the  increase  of  tempera- 
ture above  the  critical  range  and  the  duration  of  the  high  tem- 
perature; but  more  rapidly  as  a  result  of  the  increase. 

The  range  in  critical  temperatures  for  straight  carbon 
steels  is  given  in  the  equilibrium  diagram  on  page  591.  The 
range  in  critical  temperatures  for  various  alloy  steels  is  always 
supplied  by  the  manufacturer.   It  should  be  noted  that  only 
eutectoid  steels  obtain  their  maximum  refinement  of  grain  size 
upon  being  heated  through  the  Ac^  temperature.  As  seen  on 


Civil  Engr-8  B.         Assignment  24.  Page  2, 

the  equilibrium  diagram,  the  critical  range  becomes  a  single 
temperature  for  eutectoid  steels.   In  all  cases  complete  refine- 
ment is  obtained  only  when  the  constituents  pass  into  a  state  of 
solid  solution,  assuming  the  form  of  austenite.  Because  of  the 
lag  or  hysteresis  effect  the  temperature  should  slightly  exceed 
the  upper  critical  temperature  on  the  equilibrium  diagram. 

Effects  of  cooling  from  above  the  critical  range:-  Read 
Article  695.  The  size  of  the  crystals  in  the  austenite  will 
largely  determine  the  size  of  the  final  grain  structure  since  the 
grain  size  does  not  change  (decrease)  with  a  decrease  in  tem- 
perature., For  this  reason  the  steel  should  be  heated  to  as 
little  above  the  critical  range  in  temperature  as  considerations 
of  time  will  allow.  The  rate  of  cooling  through  the  critical 
range  also  affects  the  final  structure.  This  change  will  be 
discussed  under  the  subject  of  tempering. 

Effect  of  grain  size*-  Read  Article  696.  With  other  con- 
ditions the  same,  the  ductility,  toughness  and  resistance  to 
fatigue  are  increased  with  a  decrease  in  grain  size.   In  general, 
coarse  grain  size  is  indicative  of  inferior  steel.  Refinement 
of  grain  is  effected  by  working  steel  as  it  cools  to  the  Ar^ 
temperature. 

Annealing:-   Read  Article  697-  Annealing  of  steel  is 
practiced  in  order  to  accomplish  three  principal  purposes,  (a) 
to  remove  coarseness  of  grain  and  thereby  secure  a  more  desirable 

combination  of  toughness,  strength,  and  ductility;  (b)  to  re- 
lieve internal  stresses  set  up  in  the  cooling  of  castings  and 


Civil  Engr-  8B.         Assignment  24.  page  3. 

the  working  of  the  steel  in  processes  of  dra\Ting,  forging,  and 
rolling;  and  (c)  to  soften  the  steel  to  facilitate  machining 
operations  and  meet  certain  physical  requirements. 

Annealing  is  generally  applied  to  steel  castings  in  order 
to  refine  their  inherent  coarse  structure  and  thus  to  correct  the- 
lack  of  ductility  and  to  increase  the  strength.  Hot  forged 
products  are  annealed  to  refine  the  relatively  coarse  structure 
\vhich  is  caused  "by  the  high  finishing  temperature.  Cold  worked 
steel,  such  as  cold  drawn  wire,  must  be  annealed  in  order  to 
increase  or  restore  its  ductility.  The  overstrain  of  wrought 
iron  and  steel  (see  Article  671  for  wrought  iron  and  717  for 
steel)  increases  the  yield  point  and  ultimate  strength  "but  de- 
creases the  ductility.   Iron  and  steel  chains  are  frequently  sub- 
jected to  overstrain  when  links  kink  or  heavy  loads  are  suddenly 
applied.  Chains  in  constant  use  should  be  annealed  at  regular 
intervals  to  relieve  the  internal  strains.  This  practice  is 
carried  out  in  large  plants  where  chains  are  used. 

Annealing  consists  of  three  operations  (1)  heating  the 
steel  to  some  predetermined  temperature,   (2)  keeping  the  steel 
at  this  temperature  for  a  given  length  of  time,  and  (3)  cooling 
the  steel  according  to  some  predetermined  method  to  atmospheric 
temperature. 

In  order  to  soften  steel  for  machining  and  to  relieve  in- 
ternal strains  it  is  not  always  necessary  to  heat  the  steel  to  the 
critical  range.   In  the  drawing  of  wire,  in  which  the  so  called 


Civil  Engr-  8  B 


Assignment  24, 


Page  4, 


"process"  or   "works"  annealing  is  used  and  in  the  white  anneal- 
ing of  cold  rolled  steel  sheets  the  metal  is  not  heated  to  the 
critical  temperature.   This  treatment  relieves  the  strain  con- 
dition of  the  ferrite  and  restores  the  ductility.   It  does  not, 
however,  develop  the  maximum  softness  produced  in  true  annealing. 

For  true  annealing  the  steel  must  be  heated  past  its 
critical  range.  Diagram  10  on  page  627  gives  the  annealing 
temperatures  recommended  by  various  authorities.  Draw  the  lines 
to  represent  the  upper  critical  range  in  this  diagram.  The  Ar, 
line  extends  from  0-900  to  3.5%  carbon  -  750°  C.,  the  Ar_  ,, 

O—fc 

line  extends  from  the  latter  point  to  0.9  %  carbon  -  690°  C.   It 
will  be  seen  that  the  recommended  temperatures  are  well  above 
the  critical  range. 

The  time  required  for  annealing  depends  upon  the  size  of 
the  piece  and  may  range  from  several  hours  to  several  days.  The 
furnace  should  not  be  brought  above  annealing  temperatures  in 
order  to  accelerate  the  heating  of  the  interior  of  large  pieces. 
This  treatment  increases  the  grain  size  of  the  exterior,  producing 
the  harmful  results  previously  mentioned. 

There  are  three  principal  methods  of  cooling;  furnace,  in- 
sulated, and  air  cooling.  Furnace  cooling  can  be  made  the  slowest 
and  it  will,  therefore,  give  the  best  results  in  softness  and 
ductility.   In  the  process  of  insulated  cooling  when  steel  is  taken 
from  the  furnace,  it  may  be  covered  with  an  insulating  material, 
such  as  sand,  lime,  or  ashes.   In  air  cooling,  the  steel  is  re- 
moved from  the  furnace  and  allowed  to  cool  in  air. 


-,  . 


Civil  Engr-8  3r  Assignment  24.  Page  5. 

Effects   of  annealing  on  the  mechanical  properties  of  steel:- 

Read  Article  698.      In  general  annealing  reduces  the   strength  and 
hardness  of  steel, "but   increases  its  ductility  and  toughness.*     The 
actual  quantitative  changes  are  relatively  unimportant. 

Overheating  and  "burning:-     Read  Article  699.      Sometimes 
rivets  are   overheated   or  burnt o     Such  treatment  can  be  easily  de- 
tected by  microscopic  examination.     The  quality  of  burned   steel 
is  destroyed  and   it  cannot  be  restored  by  heat  treatment.      It 
can  be  made   into  steel  again  only  by  being  again  melted  and  re- 
fined. 

Theories  of  hardening  steel:-       Read  Article  700 »     The 
retention  theories  are  probably  the  most  generally  accepted  even 
though,  they  do  not  satisfactorily  explain  all  of  the  observed 
facts.     According  to     these  theories     hardened   steel  is  in  a 
state  of  unstable  equilibrium  and,  therefore,    is  tending  to 
assume  a  more  stable  form.     That  is,  the   iron  has  a  constant 
tendency  to  return  to  the  alpha  form,   and  the  carbon  to  revert  to 
segregated  cementite. 

Essentials   in  hardening:-       Read  Article   701=      Hardening 
results  from  heating  the   steel  above   its  critical  temperature  and 
suddenly  cooling  it.     Heating  is  done   in  various  ways.     For 
simple  pieces,  the   ordinary  blacksmiths       forge   is  satisfactory , 
Electric   or  gas  fired  furnaces  and  baths  are  used  when  nuch 
hardening  is  to  be  done.     Baths  of  molten  lead   or  chlorides  of 
calcium  or  potassium  are  commonly  used  for  certain  types  of 


Civil  Engn-8  B.         Assignment  H4t.  Pag$  6. 

work.  But  in  all  cases  the  steel  is  cooled  by  being  plunged  in- 
to a  suitable  liquid.  This  part  of  the  process  is  called  quench- 
ing. 

The  heating  for  hardening  is  the  same  as  that  for  true 
annealing.  Steel  will  not  harden  unless  heated  above  its  criti- 
cal temperature.   It  should  be  thoroughly  and  uniformly  heated 
at  a  slow  rate  to  the  lowest  temperature  that  will  give  the  de- 
sired results.  This  temperature  should  not  be  exceeded. 

Methods  of  hardening.   Read  Article  702.  Since  the  rate 
of  cooling  controls  the  hardening  process,  and  since  the  cooling 
medium  is  the  means  of  withdrawing  heat  from  the  steel,  its 
selection  is  of  importance.  The  various  hardening  media,  in 
order  of  their  hardening  pov/er,  are  listed  in  the  text.  The  com- 
mercial use  of  these  materials  is  also  given.  After  water  the 
chief  quenching  media  are  oils,  all  of  which  are  slower  than 
water.  Combination  methods  of  hardening,  and  their  use  and 
value,  are  discussed  -in  the  text. 

Much  skill  is  required  on  the  part  of  the  operator  in 
quenching  steel  to  prevent  warping  and  cracking.  Some  of  the 
difficulties  are  discussed  on  page  636  and  methods  for  overcom- 
ing them  are  also  given. 

Steels  containing  less  than  0. 3  %  carbon  cannot  be 
appreciably  hardened  by  ordinary  methods  of  heating  and  quenching 
because  of  the  separation  of  ferrite  from  the  solution  during 
the  process.  This  separation  occurs  even  with  the  most  rapid 
methods  of  cooling. 


Civil  Engr-8  B»  Assignment  24.  Page  7« 

Effect  of  carbon  on  hardening  :     Read  Article  703.     The 
majority  of  the  evidence  on  the  effect  of  carbon  does  not  agree 
with  Figure  21  on  page  636.     Eutectoid   steels  posses  the  maximum 
hardening  power.     The  difference   in  hardness  between  quenched 
and  unquenched  steels  of  this  composition  is  greater  than  that  of 
steels  T7ith  other  carbon  contents.     Steels  with  more  carbon, 
hyper-eutectoid   steels,  may  show  greater  hardness  both  before  and 
after  hardening  because   of  the  free  cementite  they  contain  or 
because  the  martensite  has  a  higher  carbon  content.     Hyper-eutecr 
toid   steels  gain  less  in  the  hardening  process  than  do  eutectoid 
steels. 

For  the  hardening  process  hyper-eutectoid   steels  are  heat- 
ed   just  above  the  Ac-  r>  -,     temperature.     This,   as  can  be  seen  in 

O  ~  &  *  J» 

the  equilibrium  diagram,    is  the  critical  temperature  for  eutectoid 
steel.     To  convert  both  the  pearlite  and  the  free  cementite   in 
hyper-eutectoid   steels  into  austenite     it  T/ould  be  necessary  to 

heat  them  to  a  point  above  the  A         temperature.     This  would 

cm 

cause  a  coarsening  in  the  grain  size,  an  undesirable  condition 
which  is  avoided  by  heating  only  to  the  Ac      temperature  . 

O~fe*"l 

Steel  quenched  from  the  lower  temperature  is  harder  because  it 
contains  some  free  cementite,  which  is  harder  than  martensite. 
IThen  quenched  at  the  higher  temperature  (Acm)  it  contains  all 


Microscopic   structure   of  hardened   steels:-       Study  Article 
704.      If  high  carbon  steel  is  rapidly  cooled,   say  in  brine,  a 


Civil  Engr-S  B°  Assignment  24.  page  8* 

considerable   portion  is  left   in  the  form  of  austenite.     Austenite 
is  rarely  an  ingredient  of  low  carbon  steels       at  normal  tem- 
peratures except   in  the  cases  of  some  alloys-      If  the   steel  is 
cooled  at  a  slower  rate,   the  characteristic   structure   of  marten- 
site  will  be  developed.     See  Figure  22  on  page  637»     Martensite 
is  very  hard  and  brittle.      It  is  suitable  for  sharp-edged  tools, 
"but,   on  account  of  its  brittleness,  not  for  machine  parts  sub- 
jected to  impact  o     With  slower  cooling  the  structure  known  as 
troostite   is  developed.     This   structure  gives  a  steel  that  is 
slightly  weaker  but  more  ductile  than  martensite.     Steel  com- 
posed of  troostite  or  a  mixture   of  troostite  and  martensite   is 
used  for  cutting  tools  and  machine  parts  .     With  still  slower 
cooling  the  steel  assumes  the   structure  known  as  sorbite.     This 
is  an  intermediate   structure  between  that  of  hardened  and  that 
of  annealed  steels.     This  structure  produces  steel  of  high 
strength  with  fair  ductility;     in  other  words  a  tough  steel. 


Steel  of  Ao  or  bite   structure   is  considered  to  be   ideal  for  use   in 

A 

stress-carrying  parts  of  machines  .     Annealing  produces  a  struc- 
ture made  up  of  pear  lite  and  ferrite  for  hypo-eutectoid   steel, 
and    of  pearlite  and  cenientite  for  hyper  -eutectoid   steels. 

Tempering:-     Read  Article  705     to  709     inclusive.      In  the 
diagram  in  Figure  25,     it  should  be  noted  that  as  the  weight  F 
decreases  the  end   of  the  spring  rises  to  the   indicated  positions; 
this  action  is  analagous  to  the  passing  of  the   steel  through  the 
various  transitional  stages   in  the  decomposition     of  austenite, 


Civil  Engr-8  B.         Assignment  24.  page  9. 

as  a  result  of  the  release  of  fractional  restraint. 

Fully  hardened  steel  is  too  brittle  for  use.   It  is  tem- 
pered or  draTm  to  regulate  the  hardness  and  brittleness,  to  tough- 
en it,  or  to  release  the  hardening  strains-  The  process  consists 
in  reheating  the  steel  to  some  temperature  be  lor;  the  critical 
range,  after  it  has  been  hardened.  The  tempering  of  edge  tools  is 
explained  on  page  643.  The  end  of  the  piece  to  be  tempered  is 
heated  just  above  the  critical  range  and  only  the  tip  of  this  end 
is  quenched;  then  the  desired  amount  of  heat,  as  judged  by  the 
change  in  color  of  the  cleaned  tip,  is  allowed  to  flow  into  the 
tip  from  the  uncooled  shaft.  When  the  secondary  heating  has 
proceeded  to  the  desired  point  the  influ;:  of  heat  is  stopped  by 
quenching  the  whole  of  the  heated  portion.  Care  should  be  taken 
to  avoid  a  sharp  line  between  the  hardened  and  the  unhardened 
portions  of  the  steel.  The  tool  should  be  kept  in  motion  to  pre- 
vent the  development  of  this  line  during  the  quenching  process. 
High  carbon  steels  must  not  be  kept  at  high  temperatures  any 
longer  than  necessary  because  the  carbon  is  precipitated  out  under 
great  heat  in  the  form  of  graphite  and  thus  the  carbon  content  is 
reduced •  This  occurs  only  in  the  case  of  the  presence  of  large 
amounts  of  carbon.   Silicon  also  aids  the  precipitation  of 
graphite. 

Drawing  is  usually  done  in  furnaces  or  baths  maintained 
at  the  proper  temperature0  This  temperature  is  determined  by 
pyrometers;  judging  temperature  by  color  of  the  steel  is  too 
uncertain  for  accurate  work. 


Civil  Engr-8  3.         Assignment  24.  Page  10. 

Maintaining  steel  at  the  drawing  temperature  for  a  con- 
siderable length  of  time  will  result  in  additional  temperingc 

The  details  given  in  Article  711  on  the  influence  of 
hardening  and  tempering  on  the  mechanical  properties  of  steel  can- 
not be  remembered o  Read  this  article  and  summarize  in  general 
terms  the  effect  of  this  treatment  on  steel.  Remember  that 
tempering  decreases  the  hardness  and  brittleness,  and  also  the 
tensile  strength  and  elastic  limit.   The  ductility,  as  ex- 
pressed by  the  percentage  elongation  and  reduction  in  area,  is 
increased  by  tempering. 

Toughening  consists  in  heating  the  steel  to  its  critical 
range,  quenching  it  and  then  drawing  it  back  at  a  relatively 
high  temperature  so  that  little  if  any  of  the  hardness  due  to 
the  quenching  remains.  This  practice  is  usually  limited  to  steel 
with  carbon  contents  ranging  from  .4  to  .6  f0,  that  is,  to 
medium  carbon  steels.  Toughening  produces  greater  strength  and 
ductility  than  annealing..   In  annealing;  strength  is  sacrificed 
for  ductility  and  softness-  The  quenching  retains  the  fine 
grain  size  of  austenite  so  as  to  insure  the  maximum  strength  of 
which  the  steel  is  capable.  The  drawing  process  relieves  the 
quenching  strains  without  increasing  the  grain  size.  Toughened 
steel  is  largely  composed  of  sorbite,  which  gives  the  highest 
combination  of  strength  and  ductility. 

Case  hardening:-    Read  Article  710.  Case  hardening  is 
essentially  a  special  application  of  the  cementation  process. 


Civil    Engr-8  3. 


Assignment  24. 


Page   11. 


T/Then  case  hardened,  the  products  are  partially  cartmrized  so 
that  the  exterior  case  penetrates  only  a  short  distance  "below  the 
surface  and   leaves  the   interior  unchanged.        It  is  employed     to 
give  a  hard,  v/ear -resist ing  surface  to  a  tough  core.     Low  carbon 
steels  are  used   in  this  process. 


Civil  Engr-83.  Assignment  24.  page   12. 

QUESTIONS. 

1.  Explain  why  eutectoid  steels  only  reach  complete  refinement 

in  structure  just  above  the  Ac-^  temperature. 

2.  Describe  changes  in  structure  which  occur  on  heating  hypo- 

eutectoid  steels  through  their  critical  range  in 
temperature. 

3.  Why  is  steel  annealed? 

4.  What  is  meant  by  "works"  or  "process"  annealing? 

5.  What  are  the  three  steps  in  the  process  of  true  annealing? 

6.  What  are  the  properties  of  burnt  steel? 

7.  Will  proper  heat  treatment  restore  the  quality  of  steel  that 

has  been  overheated  or  burnt? 

8.  HOT;  is  steel  hardened? 

9.  Why  cannot  lov;  carbon  steels  (such  as  structural  steel)  be 

hardened  by  ordinary  methods?  Why  is  it  necessary  to 
specify  the  method  of  hardening  of  steel  according  to  its 
use? 

10.  How  does  an  increase  in  carbon  affect  the  hardening  power  of 

steels? 

11 .  How  does  the  quenching  nedium  affect  the  hardness  of  quenched 

steel?  What  are  the  principal  quenching  media? 

12.  What  are  the  names  given  to  the  transition  stages  occurring 

in  the  process  of  the  hardening  of  steel. 

13.  What  is  meant  by  the  tempering  or  drawing  of  steel? 

14.  What  is  the  structure  of  toughened  steel?  What  are  the 

advantages  of  toughening  over  annealing? 

15=  Why  are  lor;  carbon  steels  used  for  case  hardening? 


UNIVERSITY  OF  CALIFORNIA.  EXTENSION  DIVISION 

Correspondence  Courses' 
Materials  of  Engineering  Construction 
Civil  Engr-S  B.  Professor  C-T.  Wiskocil 

Assignment  255 
EFFECTS  OF  MECHANICAL  WORK  OH  STEEL 

Effect  of  hot  -work  on  the  structure:-   Read  Article  712, 
If  steel  is  worked  at  its  critical  range  by  any  of  the  methods 
previously  discussed  the  grain  structure  -will  "be  refined.  After 
the  critical  range  has  "been  passed  additional  work  will  not  cause 
any  change  in  size  of  the  grains ,  The  refinement  of  grain 
structure  in  a  steel  casting  due  to  forging  is  shown  in  Figures  11 
and  13  on  page  628.  By  the  time  the  steel  has  "been  worked,  its 
temperature  should  be  near  the  lower  critical  value  so  that  the 
grain  structure  will  not  be  changed  by  heat  that  may  remain  in  the 
piece „  No  changes  will  occur  below  the  critical  range. 

Effects  of  hot  work  on  the  properties:-    Read  Article  713. 
Since  hot  work  during  the  cooling  of  steel  through  the  critical 
range  in  temperature  refines  the  grain  size  it  is  to  be  expected 
that  the  physical  properties  of  the  steel  will  be  improved*  Cer- 
tain examples  are  given  in  the  text.   Large  shafts  must  be  forged 
with  heavy  blows  so  that  the  effect  of  the  mechanical  work  will 
penetrate  the  material,  or  they  should  be  made  hollow  so  that  better 
metal  will  be  assured. 

Effects  of  cold  working:-   Read  Articles  714  to  717  in- 
clusive.  Steel  is  ordinarily  rolled  at  a  red  heat,  and  through  this 
process  the  strength  and  ductility  are  increased,  because  of  the 


Civil  Engr-8  3.  Assignment  25-'  Page  2 


refinement  in  grain  size,  as  previously  noted.   If  steel  is  "brought 
to  its  final  size  at  temperatures  "below  its  critical  range,  it  is 
called  cold-rolled  steel.  Working  the  steel  at  this  temperature 
increases  its  tensile  strength  and  elastic  limit  but  decreases 
its  ductility  c  The  grains  are  distorted  and  do  not  reduce  in 
size  as  they  do  at  temperatures  within  the  critical  range.  The 
distortion  of  the  grains  or  crystals  produces  internal  stresses 
that  raise  the  strength  and  elastic  limit  c  Cold  drawing  of  rods 
and  wires  has  the  sane  effect  as  cold  rolling  of  steel.  Cold  rolled 
steel  is  used  for  shafting  "because  the  process  leaves  a  smooth 
surface  and  true  dimensions  so  that  machining  is  not  necessary.   If 
machining  is  done,  such  as  cutting  keyways  or  holes,  it  is  liable 
to  distort  or  warp  the  shaft  due  to  the  redistribution  of  the 
stresses  caused  by  the  cole!  working.   Most  steel  wire  is  cold 
drawn  and  cold  dravm  shafting  may  be  obtained  up  to  3"  in  diameter. 

The  effect  of  cold  working  can  be  removed  by  annealing. 
From  previous  discussions  on  the  changes  in  grain  structure  caused 
by  annealing  the  refinement  of  structure  and  release  of  internal 
stresses  in  cold  worked  steel  can  be  readily  under  stood  »  This 
change  is  well  illustrated  in  Figure  39  on  page  659. 

Grain  growth  in  steel—    Read  Article  718.   Cold  working 
may  cause  the  growth  or  enlargement  of  crystals  in  the  case  of 
certain  pure  metals  but  not  in  the  casge'of  commercial  iron  and 
steel.   Overheating,  that  is  heating  over  the  critical  temperature, 
will  cause  increase  or  coarseness  in  the  structure  of  steelo 


Civil  Engr-8  B*          .Issigiment  25.  Page  3* 


Stead's  "brittleness  is  a  condition  caused  by  heating  from  650° 

to  750°C  for  long  periods  of  time,,   It  occurs  in  lov:  carbon 

steel  and  causes  large  crystallization  with  a  decrease  in  ductili- 

ty.  It  is  not  often  encountered  "because  the  necessary  conditions 

rarely  occur  in  practice.  Where  it  does  occur,  cthe  original  grain 

structure  can  be  regained  by  proper  annealing. 

Influence  of  form  on  properties  of  steel:-   Read  Articles 
719  to  723  inclusive  .  The  form  of  the  piece  affects  both  the  dis- 
tribution of  stress  and  the  elongation  under  tension.  These  con- 
siderations are  of  most  importance  in  design  and  investigation. 
It  is  natural  to  expect  that  where  steel  is  confined,  it  -will  have 
greater  strength  and  elastic  properties,  as  discussed  in  Article 
723.  These  matters,  however,  are  relatively  unimportant  in  a 
course  in  Materials. 

Wire  rope  :-   Read  Articles  724  and  725ii  The  properties  of 
steel  wire  are  given  in  Article  724i  Methods  of  manufacture  have 
been  previously  discussed,   plow-steel  is  one  of  the  strongest 
materials  used  in  the  construction  of  wire  rope.  The  name  originat- 
ed in  England  where  it  was  applied  to  a  strong  grade  of  crucible 
steel  wire  which  VTB.S  used  in  the  construction  of  strong  ropes 
employed  to  pull  gangs  of  plows.  At  present  it  is  used  to  designate 
a  high  grade  of  open  hearth  steel;  and  in  wire  rope  made  of  plow- 
steel,  the  tensile  strength  of  the  wire  is  about  250,000  Ib.  per 
sq.  in.  The  proportional  limit  of  plow  steel  is  about  70f0  of  its 
ultimate  strength  while  its  ductility  is  very  lor;;  the  average 


Civil  Engr-8  B.  Assignment  25.  Page  4. 

> 

percentage  elongation  is  5$.  While  ploy/  steel  is  an  unsatis- 
factory name  it  has  been  associated  with  the  trade  for  such  a 
long  time  that  it  has  come  to  have  a  fairly  definite  meaning » 

Lang-lay  rope  is  defined  in  Article  725,  The  difference 
between  this  type  of  rope  and  ordinary  rope  should  be  remembered. 
In  regular  lay  rope,  the  wires  of  the  strands  are  twisted  in  one 
direction  and  the  strands  laid  into  the  rope  in  the  opposite 
direction.  Most  of  the  rope  used  in  America  is  regular  lay  rope; 
and  rope  of  this  type  has  become  standard  for  most  work.   In  Lang- 
lay  rope  both  the  vires  in  the  strands  and  the  strands  are  in  the 
same  direction.   It  is  more  easily  untwisted  than  regular  lay  rope 
and  it  is  also  more  difficult  to  splice.   It  is  well  adapted  to 
external  wear  and  grip  action.   Its  use  is  rather  limited  compared 
to  that  of  regular  lay  rope. 

Most  rope  is  made  right  lay,  which  means  that  it  is  twisted 
to  the  right,  like  the  threads  of  a  right  hand  screw  of  long 
pitch.   The  majority  of  oil-well  drilling  ropes  are  made  left  lay. 
The  construction  is  specified  by  giving  the  number  of  strands  in 
the  rope  and  the  number  of  vires  in  each  strand.  A  6  by  19  rope 
is  one  having  6  strands  of  19  wires  each.  The  strands  are  laid 
around  a  hemp  or  manila  center  to  form  the  complete  rope.  The 
hemp  or  fiber  center  holds  the  lubricant  and  affords  a  bedding  for 
the  strands   The  life  of  a  rope  depends  on  a  number  of  factors : 
the  character  of  the  metal  used,  the  construction  of  the  rope,  the 
diameter  of  drums,  sheaves,  and  pulleys  over  which  it  operates; 


Civil  Engr-8  B  «.  Assignment  255  Page  5- 

and  to  a  great  extent     how  it   is  lubricated.     When  intended  for 
heavy  wear  the  henp  center   should  be  saturated  with  a  suitable 
lubricant.      The   lubricant  reduces  friction  between  the  component 
parts   of  the  rope  and  prevents  corrosion. 

The  diameter   of  a  rope   is  usually  baleen  a  a  the  diameter  of 
'\4s  CJrosr-Sc-dktj*.  «* 

a  circle   just  enclosing  t&firxape  ...      In  a  1  1/2  inch  rope  the 

r 

smallest  cross  -sectional  dimension  may  be  as   little  as  1  3/8  inches 


'this   latter  measurement   is  Domo  times  taken  as  the  diameter. 

A 

There  are  various  classes  of  wire  rope.     Tiller  rope  is 
the  most  flexible.      It  is  used  motly  for  boat  tillers.     Guy  rope 
is  used  for  guying  steel  stacks,   derrick  masts,   and  gin  poles/ 
and  for  similar  purposes  where  there   is  static   load  without   im-:: 
pact.      It  is  sometimes  used  also  in  hauling     where  the  ropes  are 
not  bent   over   sheaves.     The  wires  are  usually  galvanized.     Hoisting 
rope       of  crucilb$  steel     is  eommonly  used  for  mine  hoists, 
elevators,   conveyors  and  derricks.      Hoisting  rope  *>£u   plow  steel 
is  used    in  heavy  work,  as  for   instance   in  locomotive  and  wreck- 
ing' cranes,      Extra-flexible   rope   of  plow  steel       is  used  on 
steam-shovel  gear  and   in  cases  where   it  is  wound  around   small 
diameter  drums  . 

The  ratio  of  strength  of  rope  to  average   strength  of  wires 
is  usually  called  the  efficiency  of  the  rope.     This  value   ol'is 
usually  about  85^.     The   strength  of  the  rope  depends  upon     the 
material  and  method  of  its  construction  upon  its  diameter. 


Civil  Engr-8  B.  Assignment  25S  Page  6* 

THE  STRENGTH  AMD  ELASTIC  PROPERTIES  OF  iJETALS 
AT  ElEVATED  TE1.SEKATUHES 

Read  Articles  SOS  to  82.0  inclusive.  The  uses  of  metals 

under  conditions  of  high  temperature  are  listed  in  Article  809. 

« 
In  spite  of  the  importance  of  the  subject  there  has  "been  little 

systematic  research  undertaken.   In  a  general  "way,  the  diagram  in 
Figure  6  on  page  763  gives  the  results  of  investigations  so  far 
completed.   Steel  reaches  a  maximum  tensile  strength  a"bout  600° 
Fahrenheit,  and  for  temperatures  over  that  value  the  strength 
decreases  quite  uniformly  to  about  1600°  F-  at  which  temperature 
it  looses  practically  all  its  strength.   It  is  possible  that  dif- 
ferent steels  will  exhibit  different  points  of  maximum  strength  but 
in  general  the  figures  given  represent  average  conditions.  The 
ductility  decreases  until  about  600°  F.   is  reached  and  for 

higher  temperatures  it  continually  increases.  The  proportional 

gradual 
limit  and  modulus  of  elasticity  show  a/decrease  with  the  increase 

over  atmospheric  temperature.  Cast,  iron  and  wrought  iron  are 
similar  to  steel  in  their  reaction  to  elevated  temperatures. 
Brass  and  aluminum  show  a  uniform  decrease  in  tensile  strength  as 
the  temperature  is  increased. 

When  steel  is  used  at  elevated  temperatures  as  the  fire- 
box of  a  boiler  or  the  stays  in  an  open  hearth  shed  furnace  it 
is  under  stress:  investigations ,  therefore,  should  be  made  with 

long -continued  or  permanent  loads.   Up  tc  this  time  no  such 

•  ••  •  '  V 

studies  have  been  undertaken. 


Civil  Engr-3  B.          Assignment  25.  Page  7. 

Welding  of  steel:-  This  subject  is  not  discussed  in  the 
te::t.  The  welding  of  wrought  iron  urns  referred  to  in  Article  674 
on  page  606.  Steel  welding,  which  is  known  as  welding  at  plastic 
heats,  is  successfully  practiced  with  soft  steel ,  but  hard  steel 
(high  carbon)  can  be  welded  by  this  method  only  by  an  experienced  . 
operator.  Cast  iron  cannot  be  welded  by  plastic  welding,,  Plastic 
welding  is  done  in  a  forge  fire  or  by  electricity.  The  parts  to 
be  joined  are  brought  to  a  temperature  a  little  below  fusion  and 
pressed  or  hammered  together.  When  electricity  is  used  the 
method  is  called  resistance  or  spot  welding.    Pieces  that  do 
not  have  to  transmit  heavy  stresses  are  fastened  together  by 
this  method.  Pieces  which  are  later  to  be  more  thoroughly  joined 
are  often  tacked  together  by  spot  welding.  Spot  welding  is  often 
well  adapted  to  certain  kinds  of  manufacturing  operations,  such  as 
the  making  of  wire  fabric  for  concrete  reinforcement,  and  of  wire 
reinforcement  coils  for  concrete  pipe,  chain  manufacture,  and 

Ke^tis 

welding  valve  stems  to  valve  seats.  The  temperature  can  be 
closely  controlled  in  this  process. 

There  are  three  principal  methods  of  fusion  or  autogenous 
welding.   The  first  is  oxyacetylene  welding  in  which  the  metal  is 
actually  fused  by  high  temperatures  resulting  from  the  burning  of 
the  gas,  usually  acetylene,  in  a  stream  of  pure  oxygen.  The  two 
gases  are  fed  through  a  blow  pipe  torch  and  ignited  at  the  tip. 
The  high  temperature,  approximately  5000  degrees  Fahrenheit,  fuses 

MteXXt* 

a  narrow  strip  of  metal  at  the   joint  and  vmfri^o  the  parts.         A 
narrow  steel,  or   iron  rod  is  melted  in  the   joint  to  supply  additional 


Civil  Engr-8  B «          Assignment  25*  page  8° 

me tal0  Most  metals  can  be  "welded  "by  this  process. 

In  this  operation,  the  oxyaoetylene  torch  is  used  as  a 
cutting  toolo  For  this  purpose  the  oxygen  is  supplied  in  excess 
and  the  temperature  is  increased  so  that  the  steel  is  burned. 
It  is  used  in  cutting  off  lugs,  gates  and  risers  from  steel  cast- 
ings where  the  cold -saw  was  previously  used.  The  torch  has 
brought  about  large  savings  in  this  operation.,   It  is  also  used 
to  cut  up  scrap  and  wreckage  of  various  kinds,   Osyacetylene 
veld  ing  is  applicable  to  thin  plates  of  metal.   It  produces  a 
coarse  structure  since  it  is  essentially  a  casting.,  A  connon 
weakness  in  this  method  is  that  the  metal  at  the  joint  is  not 
thoroughly  welded  at  the  middlelof  the  thickness  of  the  plates. 
Joints  of  this  kind  can  be  made  so  that  the  average  efficiency 
is  about  8C^  but  as  usually  made  under  ordinary  conditions  by  the 
average  workman  the  efficiency  approaches  nearer  to  5($.  Torch 
welding  is  widely  used  in  repair  work  in  which  cast  as  well  as 
rolled  metals  are  to  be  repaired,  and  is  the  method  in  most 
general  use. 

A  second  method  of  fusion  welding  is  the  thermit  methods » 
The  necessary  temperature  is  secured  by  igniting  a  mixture  <nf 
iron  oxide  and  aluminum.  The  materials  are  ignited  in  a  crucible 
and  where  they  reach  a  temperature  of  approximately  4500  degrees 
?. ,  the  hot  metal  is  poured  into  the  joint  to  be  repaired.   It 
forms  a  casting  and  is  therefore  adapted  to  the  repair  of  heavy 
sections  such  as  locomotive  and  heavy  engine  or  machines  frames. 
Repairs  by  this  method  can  be  readily  made  in  the  field. 


Civil  Engr-8  3 .  Assignment  25.  page  9» 

A  fusion  weld  can  also  be  made  "by  the  use  of  an  electric 
arc.      The  arc   is  drawn  between  the  metal  and  an  electrode   of 
steel  or   iron  which  is  held   in  the  hand   of  the   operator.     The 
metal  to  fill  the   joint   is   supplied  partly  by  the  metal  to  be 
repaired  and  partly  by  the  electrode,  both  of  -which  are  fused  by 
the  temperature   of  the  arc,.     This  method!  cannot  be  used  in  the 
field  unless  electric  current   is  available..      It   is  an  excellent 
shop  method.      If  alternating  current  is  supplied  a  mot or -gene rat or 
set  or  rotary  converter   is  necessary  tp  produce  direct  current. 
As  reported   in  Bulletin  179  United   States  Bureau  of  Standards  on 
EIECTRIC-ARC  WELDING  OF  STEEL,   the  mechanical  properties,  as 
measured  by  the  tension  test  and  by  microscopic  examination,  v'- 
show  that  arc-fused  metal  is  an  inferior  grade.     The  ductility- 
is  particularly  low.     With  careful  manipulation  and  annealing, 
however,  very  satisfactory  welding  can  be  done  by  this  method. 


Civil  Engr-8  B 


Assignment  25 


page   10, 


QUESTIONS 


lr      In  what  -way  does  hot-work  affect  the   structure  and  properties 
of  steel? 

2*     What   is  meant  "by  cold-working?     How  does  it  affect  the 
properties   of  the  steel? 

3.      Is  it  possible  to  restore  the  original  ductility  to  cold-  drawn 
steel  wire? 

4..     What   is  plow  steel?    What   is   its  approximate  tensile   strength, 
proportional  limit,   percentage  elongation  and  modulus  of 
elasticity? 

5o     What   is  a  Lang   lay  rope? 

60     What  is  a   left   lay  rope  and  what   is   its  principal  use? 

7c     What  factors  determine  the   life   of  wire  rope? 

80     Define  efficiency  as  applied  to  wire  rope.       What  is  the  average 
e  f  f  i'ciencyT"" 

9«     Would  the   strength  of  steel  "be  affected   if  it  were  used  at  a 
temperature   of  500  degrees  F.  ? 

10.  Wha.t:.  are  the  two  principal  types  of  welding? 

11.  What  welding  process  would  you  advise  for  the  repair   of  a 

broken  locomotive  frame?     For  a  cracked  automobile  fender? 
For  filling  blow  holes  in  a  defective   steal  casting?     For 
repairing  a  wr ought   iron  tie  rod?     For  replacing  a  broken 
tooth  in  a  cast  iron  gear? 


UNIVERSITY  OF  CALIFORNIA.  EXTENSION  DIVISION 

Correspondence  Courses 
Materials  of  Engineering  Construction 

Civil  Engr-8  B.  Professor  CM.  Wiskocil 

Assignment  26 
ALLOY  STEELS 

Introduction:-    Read  Article  728*     This  may  be  said  to  be 
the  age   of  alloy  steel.      It  lias  been  demonstrated  that  the  develop- 
ment and  manufacture  of  airplanes,  automobiles,  tractors,  artillery, 
armour  plate  and  cutting  tools  would  have  been  impossible  without 
alloy  steels.     Langley's  original  airplane,  which  antedated  the 
successful  machines  of  the  Wright  brothers,   could  not     be   success- 
fully operated  because  of  the  heavy  and  inadequate  power  plant. 
It  was  recently  equipped  with  a  modern  motor  and  it  flew  perfectly. 
Early  automobiles,   commonly  known  as  horseless-carriages  at  the 
time  they  were  first  introduced,  were  cumbersome,  expensive 
devices  compared  with  the  automobile   of  today.     The  development  of 
automotive  machinery  is  thus  due  to  alloy  steel.     During  the  past 
fifteen  years  and  especially  during  the  War  many  problems  have  been 
encountered  that  could  not  be   successfully  met  with  ordinary 
carbon  steels.     The  builders   of  the   lowest  priced  automobile   in 
the  world  today,  which  contains  the  highest  percentage   of  relative- 
ly expensive  alloy  steels,   acknowledge  that   it  is  the  use  of  these 
alloy  steels  which  has  made  their  product  possible. 

High  grade   steels,    other  than  structural  grade  and  machine 
steel,  reach  the  user  in  a  condition  in  which  the  properties  are 


Civil  En^r-3  B-  Assignment  26.         .       Page  2. 

still  to  "be  developed.   In  the  case  of  carbon  steels  the  applica- 
tion and  renoval  of  heat  to  bring  out  or  develop  the  properties 
inherent  in  the  steel  were  thoroughly  discussed.  Alloy  steels  also 
require  heat  treatment  to  produce  the  physical  properties  which 
they  are  capable  of  developing. 

Many  different  alloy  steels  have  been  developed  but  relative- 
ly few  have  gained  commercial  importance .  Probably  the  first 
commercial  alloy  steel  -was  the  s3 If -hardening  tungsten  tool  steel 
developed  by  I!ushet  in  1863 c  About  fifteen  years  later  a  chrome 
steel  was  put  into  use  for  the  manufacture  of  projectiles.  Then 
in  1382  the  well-knov;n  manganese  steel  was  discovered  by  Hadfield. 
The  development  of  nickel  and  the  other  commercial  alloy  steels 
followed  the  discovery  of  manganese  steel. 

The  definition  of  alloy  steel  as  given  by  Hibbard  is  similar 
to  that  ^iven  in  the  te:rb,   "Alloy  steel  is  steel  that  contains 
one  or  more  elements  other  than  carbon  in  sufficient  proportion  to 
modify  or  improve  substantially  and  positively  some  of  its  useful 
properties". 

Ternary  Alloys 

A  simple  forn  of  alloy  steel  is  that  which  is  sometimes 
called  (as  in  the  text)  ternary  steel.   It  is  one  which  contains 
one  alloying  element  besides  carbon  and  iron.  The  term  ternary  is 
used  because  of  the  fact  that  the  steel  is  made  up  of  three 
principal  constituents,  while  the  designation  simple  alloy   is 


Civil  Engr-8  B«          Assignment  26.  Page  3. 

logical,  because  in  steel  of  this  type,  only  oue  alloying 
element  is  added  to  carbon  steel.  The  tungsten  and  manganese 
steels  previously  mentioned  are  simple  alloy  steels,, 

As  has  been  noted  in  the  discussion  on  manufacture  of 
steel,  in  all  steels  various  elements  are  added  for  curative  pur- 
poses during  the  making  process.  Uanganese  in  quantities  less 
than  1  1/2  ^  was  added  to  prevent  red -shortness ,  aluminum  is 

added  to  quiet  the  molten  steel  before  pouring,  and  other  elements 
such  as  silicon,  titanium  and  vanadium  are  added  in  small  quantities 
for  similar  reasons.  The  introduction  of  these  alloying  elements 
does  not  bring  steel  into  the  strict  alloy  steel  class.,   It  re- 
sults merely  in  what  is  called  alloy-treated  steel. 

Alloy  steels  are  usually  heat  treated  because  heat  treat- 
ment adds  to  the  superior  qualities  which  have  been  gained  by  the 
use  of  alloys .  Certain  structural  steels  ivhen  made  into  large 
units  such  as  rails  and  members  for  bridges  are  used  without  heat 
treatment.  Their  superior  properties  are  due  solely  to  the  pres- 
ence of  the  alloying  element  -  usually  nickel.  Where  practical, 
structural  steel  products  are  heat  treated.  Structural  steel 
is  used  for  stationary  and  moving  parts  of  vehicles,  machines, 
ships,  and  armor  plate,  as  well  as  for  bridges  and  buildings. 
Alloy  steels  for  cutting  tools  and  electrical  purposes  are  placed 
in  separate  classes  and  furthermore  they  are  usually  treated  with 
different  alloying  elements. 

Sometimes  alloy  steels  are  heat  treated  before  they  are 
machined.   This  process  is  very  difficult  if  the  elastic  limit  is 


Civil  Engr-8  3.  Assignment  26.  page  4. 

in  excess   of  100,000  Ib.   per  sq.    in.      It  is  claimed  that  chrome- 
vanadium  steel  can  be  commercially  machined  even  up  to  such 
strength  as  represented  "by  150,000  Ib.    per  sq.    in.   elastic   limit, 
Chrome -molybdenum  steel  is  even  more  easily  machined  than  Chrome- 
vanadium.     Ho  commercial  alloy  steels  exceed   100,000  Ib.   per  sq. 
in.    in  elastic   limit  strength  in  the  normal  state. 

Alloy  steels  are  made  by  pneumatic,   open  hearth,  crucible, 
and  electric  processes.     The   largest  tonnages  are  made  by  open 
hearth  and  electric  methods.     They  are  usually  alloys  of  nickel, 
chromium  and  vanadium. 

Nickel  Steel;-       Read  Article  792.     Nickel  steel  was  used 
for  the  first  time  about   1888.      It  aggregates  a  large  tonnage  at 
the  present  time  but  the  field  is  being  reduced  by  the  cheaper  and 
in  some  trays  better  chrome -nickel  steels.     ££a!lost  of  the  straight 
nickel  steels  are  made  by  open  hearth  methods.     Additions  of  leas 
than  2$  nickel  are  not  v;orth  the  extra  cost.     Useful  nickel 
steels  range  from  about  2     to  46$  nickel.     This  is  a  voider  range 
than  has  been  found  for  any  other  alloying  element.     Untreated 
nickel   steel  has  higher  elastic   limit  and  ultimate   strength  than 
similar  carbon       steel  without  nickel,  but  practically  the   same 
ductility.     Heat  treatment  increases  the  strength  of  nickel  steel, 
both  elastic   limit  and  ultimate,  but   it  also  decreases  the 
ductility. 

Nickel  may  be  added  to  the   steel  at  any  time   just  so  that 
it  has   opportunity  to  becorae  thoroughly  diffused  throughout  the 
melt  before   it  is  poured.      It   is  usually  added  to  the  bath  just 


Civil  Engr-  8  B.          Assignment  26.  page  5» 

before  it  is  tapped.   It  is  not  added  for  curative  purposes;  it  is 
preeminently  a  strength  giving  element.  Unfortunately  nickel  steel 
is  subject  to  cortain  defects  such  as  seams  and  surface  marks, 
which  limit  its  user 

Ordinary  niche  1  steel  contains  from  3  to  4  %  nickel.  T3hen 
the  percentage  of  nickel  is  not  specified  in  an  order  steel  contain- 
ing about  3.25  %  is  furnished  since  this  percentage  produces  the 
best  properties  for  most  structural  purposes.  This  type  of  nickel 
steel  is  well  adapted  to  service  conditions  that  are  too  severe  for 
ordinary  carbon  steel,  such  as  in  certain  kinds  of  bridges,  gun 
forgings,  engine  and  automobile  parts,  and  large  dynamos. 

In  the  range  used  in  ordinary  nickel  steel  (2  to  4$)  each 

€A\ 

addition  of  \%  nickel   increases  the  tnfrsile   strength  about     6,000 

lb<,   per  sq.    in,    over  carbon  steel,  -without  affecting  the  ductility- 
This   increase   occurs  through  the  additions  of  nickel,  without 
heat  treatment.     The  use  of  nickel  saves  some  weight,  which  is  a 
factor   in  the  construction  of  long   span  bridges  such  as  the  Quebec 
bridge   in  which  untreated  nickel  steel  was  used.      Steel  having  about 
So  5f0  nickel  is  good  case  hardening  stock. 

With  the  addition  of  from  5  to  8  %  nickel  the  metal  becomes 
very  hard  and   is  difficult  to  work  in  both  the  hot  and  cold  con- 
ditions.     Its  principal  use   is  for  the  manufacture   of  thin  armor 
plates  which  are  used  for  protecting  field  artillery  from  rifle 

fir*. 

Steels  containing  about  10  fa  nickel  cannot  be  hardened  by 

quenching . 


Civil  Engr-8  B.  Assignment  26.  Page  6. 

In  1914  a  steel  containing  12%  nickel  and  .55$  carbon  was 
discovered  which  had  a  yield  point  of  about  134,000  and  an 
ultimate  tensile  strength  of  195,000  Ib.  per  sq.  in.  This  alloy 
of  nickel  is  thought  to  be  the  strongest  in  the  entire  series  of 
nickel  steels.   It  is  very  hardc   It  cannot  be  machined  or 
drilled.   Its  elongation  is  about  12  $.   Its  commercial  use  is 
very  limited;  it  is  only  made  into  shafting  to  replace  shafts 
made  of  other  steels  that  could  not  withstand  the  particular 
service  conditions- 

Steels  containing  about  22$  nickel  have  high  rust  resist- 
ing qualities.   Steels  having  from  24  to  32$  nickal  are  used  for 
electric  resistance ,  in  such  articles  as  electric  iron,  toasters, 
and  other  household  heaters. 

Invar  steel,  which  contains  36$  nickel,  is  mentioned  in  the 
te;rt.  Not  more  than  a  few  hundred  pounds  a  year  are  used;  yet 
in  certain  industries  it  is  important.   Its  principal  uses  are 
listed  in  the  text.   Some  invar  tapes  have  been  made  with  coeffici- 
ents of  thermal  expansion  as  low  as  ,0000008  per  degree  centigrade, 
This  means  a  change  of  0.05  inches  per  mile  for  one  degree  centi- 
grade change  in  temperature-   Some  invar  steels  have  been  found 
to  have  negative  coefficients;  that  is  they  actually  contract  when 
heated «. 

Platenite  is  also  mentioned  in  the  text.   It  contains  46$ 
nickel  and  .15$  carbon.   It  was  at  one  time  more  used  than  it  is 
w.,  principally  for  wires  which  lead  into  electric  lamp  bulbs. 


Civil  Engr-8  B.          Assignment  26.  Page  7. 

It  was  a  substitute  for  platinum.  Other  alloys  are  now  replacing 
platenite  for  the  purpose  mentioned. 

There  are  other  alloys  of  nickel  "but  they  are  of  scientific 
interest  only. 

Ilanganese  steel;-    Read  Article  730.  Commercial  man- 
ganese steel  contains  from  11  to  14$  manganese  and  from  1.0  to 
1.3  f0  carbon.  Host  of  the  manganese  steel  produced  is  made  into 
castings.  The  field  for  manganese  steel  is  not  very  large  and 
there  are  relatively  few  concerns  making  it.  About  six  companies 
in  United  States  supply  practically  all  that  is  made. 

i&nganese  steel  is  made  by  the  pneumatic,  open  hearth,  and 
electric  processes.   In  the  process  of  manufacture,  ferromanganese 

is  added  to  the  decarburized  metal.  This  supplies  all  of  the 
manganese  and  practically  all  of  the  carbon,  in  the  finished  metal. 
Ilanganese  steel  cannot  be  successfully  made  from  manganese  steel 
scrap.  On  the  whole  it  is  more  difficult  to  make  and  cast  than 
carbon  steel.  At  the  present  time  it  cannot  be  commercially 
machined.   It  is  used  for  jaws  of  rock  cmafchers,  for  rails, 
frogs  and  crossings  for  railroad  work,  and  also  for  burglar-proof 
safes.  These  safes  are  made  of  a  laminated  construction  having 
alternate  layers  of  hard  and  soft  steel  thus  making  it  difficult 
for  a  drill  to  penetrate .  Manganese  steel,  as  well  as  all  other 
kinds,  however,  can  be  readily  cut  with  an  oxyacetylene  flame. 
Ilanganese  steel  has  a  low  yield  point.   Under  many  field  condi- 
tions it  peens-out  or  flows  under  repeated  blows.  This  makes 


Civil  Engr-8  B.  Assignment  26=  Page  8. 

it  unsatisfactory  for  uses  for  -which  its  high  abrasive   resistance 
would   otherwise  make  it     preeminently  successful.     Manganese 
steel  for  buckets   in  gold  dredgers   is  "being  replaced  by  other 
alloys  with  higher  elastic   limits.     The  breaking  of  a  bucket  line 
causes  expensive  delays  and  a  reliable  product  is  required.      It 
is  more  difficult  to  obtain  uniform  material  and   finished  castings 
in  manganese  stael  than  in  other  types  of  alloy  steels.     The 
principal  demand  for  hot-rolled  manganese  steel  is  for  use  as 
railroad  rails.. 

Chrome  steels;-         Read  Article  731.      Steels  alloyed  -with 
chromium  have   great  strength  and  hardness.      Chrome  steels  are 

cast,   rolled  and   forged  just  as  carbon  steels  are.     They  are 
rarely  used   in  the  untreated  condition.     Chrome  steels  have  been 

used  for  stamp  shoes   in  pulverizing  gold  and  silver   ores,  and  for 
safes.     Some  chrome-steel   is  also  made   into  files  and  balls  and 
rollers  for  bearings.        Simple  chrome  steel  was   one   of  the  first 
alloy  steels: commercially  used. 

Chromium,   hot/ever,   is  usually  alloyed  with  other  elements 
to  form  quarternary  alloys. 

Quartenary  Alloys 

Tungsten  steel:-     Read  Article  732.      Simple  tungsten  steel 
is  noV becoming  obsolete.      It  was   important  at   one  time  and 
formed  an  important   stage   in  the  development  of  high-speed  tool 
steels.      Ilushet's  air-hardening  steel,  while   it  contained  6f0 
tungsten  and  2  %  manganese   -  the   latter  added  to  give  it  the 


Civil  Bngr-8  B.  Assignment  26.  Page  9. 

self  hardening  property  -  iras  usually  classed  as  a  simple 
tungsten  steel. 

Vanad ium  Ste e 1 ; -       Read  Article  733.     Vanadium  adds  great 
strength  to  steel  and  makes   it  free  from  flairs  and   seams .      It  is 
used   in  high  spaed  steels.      It  is  not  used  much  as  a  simple  alloy 
"but  usually  is  combined  with  chromium.     Chrom- vanadium  steels  are 
used  principally  for   locomotive  forgings,   automobile  springs  and 
axles  and  gun  forgings. 

Silicon  steeds :-       Read  Article  734.     Silicon  is  an  ingredi- 
ent  of  practically  all  steels.      It   is  added  to  tool  and   structural 
steels  to  promote  soundness,   and   is  added   just  before  the  metal 
is  teemed,   and  should  preferably  be   in  a  molten  stats .     The 
principal  use  for   silicon  steel  is  in  the  manufacture  of  leaf 
springs  for  automobiles. 

Chrome-nickel  steel:     Ores  found  near  llayari,  Cuba, yield 
a  natural  chrome-nickel  steel,     llayari  steel,  as  this  product  is 
called,  has  been  found  to  have  excellent  qualities  for  certain  pur- 
poses;  but     it  is  generally  inferior  to  synthetic  chrome-nickel 
steels.      This  type   of  alloy  steel   is  vridely  used   in  the  manufacture 
of  automobile  parts  and  for  arraor  plate  and  armor  piercing  pro- 
jectiles.    Chrome-nickel  shafts  and  gears  have  excellent  -wearing 
qualities. 

Chrome -vanadium  steel:-  Read  Article  736.  Chrome -vanadium 
steels  are  made  in  the  open  hearth  furnace  and  the  alloying  elements 
are  ;.  jadded  just  before  casting.  Chrome -vanadium  steels  slightly 


Civil  Engr-8  B .  Assignment  26*  Page   10. 

surpass  chrome -nickel  steels   in  physical  properties.     Most  of  the 
output  goes   into  the  manufacture   of  automobiles.     Vanadium  is  a 
strong  deoxidizer  while  nickel  is  not.     Vanadium  steels  are, 
therefore,,  more  free   from  surface  imperfections  such  as  seams     than 
are   steels  which  contain  nickel. 

I!o lybd e nuis  steel:-       Molybdenum  is. added   in  the  form  of 
ferro-molybdenum  or  calcium  molybdate.     The  final  molybdenum 
content  of  the  present  commercial  molybdenum  steels   is  less  than 
\%*  Since  the  YJar  molybdenum  steels  have  become  commercially 

important.      They  v/ill  probably  soon  replace  chrome -nickel  and 
chrome -vanadium  steels  v/hich  are  now  so  generally  used  in       auto- 
mobile construction.     During  1921     the  Studebaker  Corporation 
used   over  2,000  tons  of  molybdenum  steels.      The  high  grade  Willis 
Sainte -Glair  automobile   is  made   largely  of  molybdenum  steel. 
Chrome-molybdenum  steel  is  more  easily  machined  than  the  nickel 
and  vanadium  alloys     of  chromium. 

During  the  ¥ar  molybdenum  vras  used  as  a   substitute  for 
tungsten  in  the  manufacture   of  tool  steel   (high-speed).     Its  largest 
use  was  for   light  armor  plate,  and  vital  parts   of  airplane  motors 
and  automotive  vehicles* 

For   its  high  strength  chrome -molybdenum  steels  have  great 
ductility.     Automobile  parts   such  as  axles  and   shafts,   made   of 
molybdenum  steel  can  be  distorted  and   twisted  without  rupture. 
Heat  treated  chrome -molybdenum  steel  has  the  following  approximate 
strengths;        140,000  Ib.    per  sq»    in.    elastic   limit,    150,000  Ib. 


Civil  Engr-8  B.  Assignment  26.  Page  11. 

per  sq.  in.  ultimate  tensile  strength,  18$  elongation  and  60$ 
reduction  in  arear 

High-speed  steels;-   The  presence  of  tungsten  or  molybdenum 
in  steel  affects  its  critical  temperature.  With  proper  heat  treat- 
ment steels  containing  these  alloys  retain  their  hardness  and 
consequently  a  cutting  edge  at  a  red  heat.  One  form  of  heat  treat- 
ment is  the  heating  of  the  steel  to  incipient  fusion,  and  quench- 
ing in  oil.      Tungsten,  molybdenum,  cobalt  and  vanadium  are 
those  alloys  used  in  the  manufacture  of  high-speed  steels,  which 
are  usually  made  by  the  crucible  or  electric  process. 

Stellite,  a  competitor  of  high-speed  steels,  is  not  a  steel, 
being  composed  of  approximately  60$  cobalt,  11$  chromium,  23$ 
molybdenum,  the  remainder  being  manganese,  iron,  carbon,  etc. 


Civil  Engr-8  Be  Assignment  26.  page   12. 


QUEST IOWS 


What  is  an  alloy  steel? 


2.  What  was  the  first  commercial  alloy  steel  and  what  was  it 
used  for? 

SB  What  is  a  ternary  alloy  steel?  Name  several. 

4.  ¥hat  processes  are  used  in  the  manufacture  of  alloy  steels? 

5.  What  is  invar  steel?  Give  its  composition  and  principal 

uses, 

6.  What  is  the  percentage  of  nickel  in  simple  nickel  steel  used 

for  ordinary  structural  purposes?  Why  is  this  steel  better 
than  carbon  steel? 

7r  What  is  the  range  in  manganese  in  commercial  manganese  steels? 
What  are  the  outstanding  properties  of  this  steel?  What 
are  some  of  its  uses? 

8.  What  is  Eayari  steel? 

9.  What  are  the  principal  alloy  steels  used  in  the  automobile 

industry? 

10.  What  is  the  advantage  of  vanadium  over  nickel  in  quarternary 

alloys  using  chromium? 

lie  What  are  the  particular  advantages  of  chrome -molybdenum 
steels?  What  are  the  uses  for  this  steel? 

12 o  What  is  meant  by  a  high-speed  steel? 

13.  Explain  why  high  speed  steels  retain  their  hardness  at  high 

temperatures. 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 
Corr e  spondence     Cour  se  s 

Materials  of  Engineering  Construction 

Assignment  27 

Civil  Engr-8B  Professor   C.   T.  Wiskocil 

CAST     IRON 

Importance  of  cast   iron:     Read  Article  738,  which  gives  the 
principal  uses  for  cast  iron.     In  building  construction  it  is  not 
as  -widely  used  as  steel;   its  greatest  field  of  use  is  in  machine 
construction.     As  indicated  in  this  article,  however,  other  metals 
must  also  be  frequently  used  in  machine  construction  because  cast 
iron  does  not  adequately   supply  the  necessary  qualities.     These 
competing  materials  are  malleable  cast  iron,   cast   steel,   and  cast 
brasses,  bronzes,  and  other  alloys. 

Cast  iron  has  a  comparatively  coarse  crystalline    structure, 
as  sho\vn  in  Figure  4  on  page  697*     It  is  readily  cast  into  useful 
shapes  and  is  easily  machined,  but  is  lacks  toughness  and  ductility. 
It  has  considerable  hardness  but  cannot  be  deformed  by  forging 
without  being  broken.     Its  constitution  is  very  complex,  and  it  is 
subject  to  much  variation  resulting  from  relatively  minor  changes 
in  the  detai 1 s  of  manuf actur ing . 

Manufacture  of  cast  iron:      Study  Articles  739  to  743  inclusive. 
When  pig   iron  is  remelted  and  cast   into  final  form  it   is  called 
cast   iron.      See  the  definitions  previously  given  on  page  586.     A 
limited  amount  of  ironAcast  directly  from  the  molten   state  as  it 
comes  from  the  blast  furnace.      Ingot  molds  are  made  in  this  way. 


Ci.vil  Engr-8B«     Materials  of  Engineering  Construction.     Assignment  27,  page  \ 

Most  cast   iron  is  made,   hoover,  by  a  mixture  of   scrap   iron  with 
pi'g  ?ron.     The  reasons  for  r erne It ing  pig  iron  and  mixing  different 
grades  of  iron  and   scrap  are  given  in  Article   739.     Most  cast  iron 
is  made   in  this  manner;   either  the   cupola  or   air  furnace   is  used. 

The  materials  used  in  the  manufacture  of  cast  iron  are  de- 
scribed breifly   in  Article  740.     The  major  portion  of  the  charge 
in  the  furnace  usually  consists  of  foundry  pig  iron*     The  amounts 
of  the  constituents  usually   specified  are   listed  on  page  540, 
Article  582.     Most  foundry  pig  is  bought  on  the  basis  of  its  analy- 
sis.    Bessemer  pig,  ferro-silicon,   and  other  materials  mentioned 
in  the  text  are  used  to  bring  the  final  composition  of  the  cast 
iron  to  desired   limits.      Some  classes  of  castings  are  made  without 
scrap  while  others  contain  as  much  as  40$   scrap.     The  term  "scrap" 
includes,  besides  worn  and  discarded  iron  castings,   defective 
castings,   gates,    sprune  s,   risers,   and  other  pieces  of  iron  re- 
claimed in  cleaning  up  castings. 

The  flux  is  used  to  form  a   slag  and  carry  off  the   impurities 
and  non-metallic  residue.      Since  the  amount  of  impurities  is  small 
the  amount  of  flux  required  is  also   small,  being  ordinarily  about 
1$  of  the  weight  of  the  iron  charge.     Calcium  carbonate  usually  in 
the  form  of  limestone   is  used  as  a  flux  but  marble,   dolomite,   and 
oyster    shells  are    sometimes  added  to  the  charge. 

The  fuel  is  used  to  melt  the  iron.  Coke  is  most  commonly  em- 
ployed but  mixtures  of  coke  and  anthracite  coal  are  sometimes  used 
in  cupolas.  Gas  and  bituminous  coal  are  used  in  the  air  furnaces. 


Civil  Engr-SB*     Materials  of  Engineering  Construction.     Assignment  27,  page 

The  fuel  requirements  are  determined  by  the  type  of  castings 
to  "be  made,  thin  castings  requiring  a  more  fluid  and  therefore  a 
hotter  metal  than  that  necessary  for   large  thick  castings. 

A  typical  cupola  furnace   is  shown  in  Figure   1  on  page  689. 
It  is  essentially  a   small  blast  furnace.     Only  a  light  blast  is 
used,  and  no  attempt   is  made  to  attain  reducing  conditions  required 
in  the  regular  blast  furnace.     The  only  function  of  the  cupola  is 
to  melt  the  charge.     The  proportion  of  fuel  to  iron  is  usually 
about  20^, 

The  usual  type  of  air   furnace  is  illustrated  in  Figure  2  on 
page  690.     The  heat  from  the  fuel  passes  over  the  bath  and  is  re- 
flected by  the  roof  of  the  furnace.     For  this  reason  it  is  some- 
times called  a  reverberat>ory  furnace.     An  air  furnace  resembles 
the  puddling  furnace  used  in  the  manufacture  of  -wrought  iron.     The 
copula  is  used  for  melting  iron  for  gray  iron  castings  T?hile  the 
air  furnace   is  used  in  the  production  of  vhite  cast   iron  for  mal- 
leable cast   iron  and  for  cast   irons  of    special  compositions. 

The   open-hearth  furnace   is  used  to  a   limited  extent   in  the 
manufacture   of  cast   iron.      It   is  more  economical  in  the   consumption 
of  fuel  than  the  air  furnace  -  but  to  be  used  to  advantage   it  must 
be  operated  continuously.     This  requires  a  large  floor    space  for 
molding  and  a  l^rge  output  of  cast   iron- 
Study  Article   743   on  the   comparison  of  the   cupola  and  the   air 
furnace.     The   air  furnace  uses  about  ttrice  as  much  fuel  as  the 


il  Engr-8B.  Materials  of  Engineering  Construction*  Assignment  27 ,  page  4. 

cupola  "but  it  produces  purer  metal  and  in  larger  quantities.  Both 
types  of  furnace  are  widely  used. 

Molding  o£  cast  iron:  Read  Articles  744  to  749  inclusive. 
Only  in  the  case  of  the  chilled  castings  is  the  quality  of  the 
metal  affected  by  the  mold.  Under  normal  conditions  of  cooling  the 
quality  of  the  metal  depends  upon  its  composition. 

The  molding  of  cast  iron  is  of  importance  to  the  engineer  and 
machine  designer.  The  pattern  must  be  so  designed  j?hat  it  can  be 
removed  from  the  sand  and  leave  the  mold  intact  and  the  shape  of 
the  casting  must  be  so  designed  that  dangerous  shrinkage  stresses 
are  not  set  up  when  the  casting  cools«  The  three  methods  -  green- 
sand,  dry- sand,  and  loam  molding  -  are  all  explained  in  the  text. 

Patterns  are  divided  into  two  classes.  In  the  first  class, 
which  includes  most  of  the  castings,  the  patterns  are  solid.  In 
the  other  class  the  hollow  part  is  formed  by  a  core  which  is  in- 
serted in  the  mold  after  the  pattern  is  removed.  The  materials 
from  which  patterns  and  cores  are  made  are  described  in  the  text 

The  use  of  chills  is  described  in  Article  748.  They  are  used 
to  produce  a  hard  wearing  surface  on  such  castings  as  rolls  and 
car  wheels.   Chilled-iron  car  wheels  are  cast  with  a  chill  against 
the  tread  and  the  inside  of  the  flange,  the  remainder  being  in  sand. 
The  composition  of  the  metal  is  such  that  under  the  imposed  condi- 
tions the  metal  against  the  chill  will  show  white  iron  to  a  depth 
of  about  7/8  of  an  inch,  the  remainder  of  the  wheel  being  graphitized 
or  gray.   So  as  to  relieve  the  severe  cooling  stresses  the  wheels 


Civil  Engr-8B.     Materials  of  Engr.   Construction-*     Assignment  27,  page  5. 

are    stripped  from  the  mold  while   still  red  hot  and  placed  in  a 
soaking  pit  where  they  are  allowed  to   cool   slowly.     A  maximum  tem- 
perature of  about  725  degrees  Centigrade  has  been  found  to  be    sat- 
isfactory for   this  annealing  process.      If  the  temperature   is  higher 
an  under  sirable  formation  of  graphite  occurs  within  the  xvhite  tread. 
The  effect  of  chills  on  the   structure  of  cast  iron  is  shown  in 
Figure   '6  on  page  6S5. 

The   cleaning  of  castings  is  described  in  Article  749.     The 
three  methods  are  rattling,  pickling,   and  sand  blasting.     Rattling 
is  satisfactory  only  in  the  case  of  the    simplest  castings.     Pick- 
ling is  in  more  general  use;   and   sand  blasting  is  most  convenient 
for   large  castings.     Often  the    sand  blast  is  followed  by  pickling. 
In  all  these  methods,  the  final  cleaning  operation  is  the   smoothing 
of  irregularities   such  as  are   left  where  gates  and  fins  have  been 
broken  off.     This  is  done  with  a  cold  chisel,  with  a  pneumatic 
chipping  tool,  or  an  emery  wheel. 

Composition  and  constitution  of_  cast   iron;     Read  Article  s 
750  to  758  inclusive.      Cast  iron  is  a  complex  alloy  composed  of 
six  important  elements  -  iron,   carbon,    silicon,  phosphorus,    sulphur, 
and  manganese;   other  unimportant  elements  are  often  present.     The 
most  important  element  is  carbon  because  of  its  pronounced  effect 
on  the    strength  of  cast   iron.     It  occurs  free  as  graphite  and   in 
the  combined  form  as  cementite    (FegC)  which  is  sometimes  called 
iron  carbide   or   combined  carbon.     The   importance  of  the  other 


Civil  Engr-8B.     Materials  of  Engr.   Construction*     Assignment  27,  page  6 

elements  is  due  to  their  influence  upon  the  carbon.     There  are 
three  distinct  classes  of  cast   iron,   depending  upon  the    state   in 
which  the   carbon  occurs.      In  gray  cast  iron  the  carbon  occurs  chiefly 
as  free   carbon  in  graphite  flakes.     In  white  cast  iron  it  is  prin- 
cupally   in  the  combined  form,  while 'in  mottled  cast  iron  there   is 
a  mixture  of  particles  of  gray  and  white   iron.     A  product  of  the 
air  furnace  or   cupola  containing  from  20  to  50$  steel   scrap  is 
known  by   the  misleading  trade  name  of   semi-steel   (see  definition 
on  page  588).     The  metal  is  actually  a  fine  grained  cast  iron.     It 
is  much   stronger  than  ordinary  cast  iron  but  it  is  not   steel.     It 
is  used  v;here  a   strong,   close  grained  metal   is  required,   as  in 
hydraulic  cylinders;   and   in  parts  requiring   strength  and   shock  re- 
sisting ability,   as  in   shear  and  punch  frames. 

The  composition  and  the  rate  of  cooling,  through  the  range  of 
solidification  and  immediately  below  that  temperature  determine 
whether  a  given  mass  of  molten  cast  iron  will  be  gray,  white  or 
mottled.     The  more  rapid  the  cooling  the   less  the  graphitization 
(white  cast  iron,  for  instance,  made  by  chilling  the  molten  irori)- 

Carbon  in  cast  iron  is  discussed  in  detail  in  Article  751. 
The  range   in  carbon  content  for   commercial  cast  irons  was  given  on 
the  equilibrium  diagram  for   iron  ^nd  carbon.     The    strength  and 
other  properties  of  the  casting  are  dependent  upon  the  form  in  which 
the  carbon  occurs.     Figure  6   (after  Howe}  on  page  699,    shows  the 
effect  of  graphite  and  combined  carbon.     The   important  features  in 


Civil-Engr-8E«     Materials  of  Engr»   Consturction..    Assignment  27,  page  7. 

this  diagram  are:     the  names  of  the   cast  irons  in  the  upper  part 
of  the  diagram;   the  tenacity,   ductility,   and  hardness  of  the  whole 
with  ordinates  and  abscissaes  in  the   central  portion;   and  all  of 
the   lower  part  of  the  diagram.     In  this  latter  portion,  note  that 
mottled  cast  iron  is  not  alluded  to  except  to    state  that  it  is 
harder o     Irons  of  this  type  have  no   special  adaptation  and  their 
production  is  not  intentional. 

Graphitization,  that  is  the  decomposition  of  the  combined  car- 
bon to  form  graphite,   is  facilitated  by    increased  carbon  or   silicon 
content  and  by   slow  cooling.     Graphitization  is  retarded  by   sulphur, 
excess  manganese,   and  rapid  cooling*     This  is  a  brief   summary  of 
Article  751.     The  effect  of  the  various  elements  will  be  discussed 
separately  in  detail. 

Silicon  in  cast   iron   is  discussed  in  Article  752.     It  ranks 
below  iron  and  carbon  in  its  importance  as  a  constituent.     The 
amount  of   silicon  in  cast   iron  can  be  controlled.      It  acts  prin- 
cipally as  -"•-  precipitant  of  graphite,   causing  a  maximum  precipita- 
tion when  about  a  quantity  of  5%.     Below  3^  it  will  aid  in  the 
production  of   gray  iron,  but  over  3%  causes  iron   silicide,  which 
results  in  a  hard  brittle  metal.      Small  amounts  decrease    shrinkage 
and  minimize  blowholes- 

The  effects  of   sulphur   are  discussed  in  Article   752.     As  in 
the   case  of    silicon  the  amount  of   sulphur   in  the  cast  iron  can  be 
controlled  during  the  manufacturing  process.     Sulphur  has  a  decided 


Civil  Engr.   SB.     Materials  of  Engr.   Construction.     Assignment  27,  page  8. 

effect  upon  the  properties  of  cast  iron.     It  prevents  graphitiza- 
tion  and  produces  hard,  "brittle  iron.     Specifications  limit  the 
sulphur  content  to  0.1$  and   some  even  to  as  little  as  0.50^.     Sul- 
phur causes  red- shortness  and  blow-holes.     It  is  an  undesirable 
element.     The  effect  of   sulphur  can  be  neutralized  by   silicon  and 
manganese,     About   15  parts  of   silicon  or  tv/o  parts  of  manganese 
are  required  to  neutralize  one  part  of   sulphur* 

In  the  best  grades  of-  gray  iron  the  phosphorus  content  is 
limited  to  O.SJb.     High  phosphorus  causes  cold- shortness.     But  when 
fluidity   is  important,   as  in  the  pouring  of  thin  castings  which 
must  have  a  good  impression  of  the  mold,   and  where  toughness  is 
not  required,  about   1.0^  phosphorus  is  used.     The  amount  of  phos- 
phorus cannot  be  controlled,   5t   is  determined  by  the  amounts  present 
in  the  materials  from  which  the  cast  iron  is  made. 

When  manganese  is  present  in   small  amounts  it  combines  with 
the    sulphur  to  form  manganese    sulphide  and  tends  to  decrease  the 
hardness  and  brittleness  of  the   iron;  but  in  greater  quantities  it 
causes  increased  hardness. 

The  other   elements  that  may  be  present  in  cast  iron  are  of 
importance  to  the   iron  manufacturer  but  not  to  the   student  of  a 
general  course   in  Materials.     Article  758  with  Table   1  can  be  onitted 
since  the  approximate  allowable  proportions  of  the  various  elements 
have  already  been  discussed  and  the   student  therefore  has  a  general 
idea  of  the  composition  of  good  cast   iron. 


E:igr-8B-     Materials  of  Engr.   Construction.     Assignment  27,  page  8. 

Read  Article  757  on  defects  and  remember  what  the  principal 
defects  are  and  how  they  are  caused. 

PROEBRT J1RS_  0£  OAST    IRON 

Shrinkage:     Read  Article  759.     The  pattern  maker  must  make 
allowance  for    shrinkage  and  the  designer  and  the  iron  founder  must 
consider  this  phenomenon  "because  of  the   induced   stresses  and  con- 
sequent danger  of  checking.     It   is  usually  assumed  that    shrinkage 
is  about   1/8  of  an  inch  per  foot.     It  is  quite  variable,  the 
chief  factors  vrhich   influence   it  being  the  presence  of    silicon,  the 
rate  of  cooling,   and   size  of  the  cross- sect ion  of  the  casting. 

Hardness:     Read  Article  760.     Hardness  is  the  term  generally 
used  to  designate  that  quality  which  has  to  do  with  the  resistance 
of  a  metal  to  cutting  or  machining,   or  to  xvearing  or  abrasion.     As 
shown  in  Figure  5  on  page  699,  the  hardness  increases  directly 
vrith  the  amount  of  combined  carbon.     This  may  be   due  to  the  hardness 
of  the   cement ite   itself  and  to  the  decrease   in  graphite  which  acts 
as  a  lubricant  to  the   cutting  tool.     Hardness  is  measured  by  the 
drill  test  and  the  ball-indentation  test.     Both  are  empirical. 
Review  Article   129  on  page   127. 

Tensile    strength:     Article  761  is  relatively  unimportant. 
Tensile    strength   is  important  but   in  a  direct  test   it   is  difficult 
to  determine.     For  average   gray  iron  the  ultimate  tensile   strength 
is  about   20,000   Ib.  per    sq.    in.      Omit  the   tables  on  pages  707  and 
708.     Remember   the  typical    stre ss-def ormation  curves  on  page  709. 


01;?.l  Fr.'.g."«8}3.     Materials  of  Engro   Construction..   Assignment  27,  page   9. 

They   show  that  ca»~t   iron  has  no  proportional   limit.     It   is  important 
to  not ^  that   cast  iron  is  weakest   in  torsion.      In  torsion  or  com- 
er nad   stress  the  piece  vill  fail  in  tension  and  its  strength  will 
be   limited  "by  the  tensile    -stcpngth  of  the  metal. 

Compressive    strength:     Read  Article  763 o     The   average  compres- 
sive    strength  of  ordinary  gray  cast  iron  at  the  proportional  limit, 
or  yield, point,   as  it   should  more  properly  be  called,   is  about 
30,000   Ib.  per    sq.   in.     The  ultimate    strength  is  about  70,000  Ib. 
per    sq*   in.     Figure   11  on  page  710  represents  a  typical   stress- 
deformation  curve. 

Transverse    strength :     Read  Article  764.     The  arbitration  bar 
is  described  in  this  article.      It  is  the  most   important  test   speci- 
men of  cast  iron.     Under    standard  conditions  an  arbitration  bar  of 
average  gray  cast   iron  \vill  give  a  modulus  of  rupture  of  about 
45,000   Ib.  per    sq.   in.     This  test  gives  a  valuable  criterion  of  the 
quality  of  the  metal.      It   is  necessary  that  the  conditions  for  the 
test  be    standardized,  because  the    size  of   specimen  and  its  method 
of  preparation  affect   its  strength.     The  removal  of  the    skin  by 
machining  decreases  the    strength,  while  tumbling  hardens  the    skin 
and  increases  the    strength. 

The  A.S.T.M.  minimum  requirements  for  the  modulus  of  rupture 
in  the  test   of  the  regulation  arbitration  bar   are   39,000.,   45,000 
and  50,000   Ib.  per    sq.    in-,   respectively,   for   light,  medium,    and 
heavy   castings.     The  minimum  deflection   is  1/10  of  an  inch. 


inl  Engr«3B.     Materials  of  Engr  »   Construction.     Assignment  27,  page   10 

Modulus  of  elasticity:     Read  Article  765.      The  modulus  of 

G&o 
elasticity  of  cast  iron   is  quite  variable;    15,000)Klb.  per    sq.   in. 


nay  be  taken   as  the  average* 

Articles  766  to  771   inclubive  are  relatively  unimportant. 
Remember  that  the    shearing   strength  of  cast   iron  is  greater  than 
its  tensile    strength.     When   subjected  to  torsion  cast   iron  fails 
in  tension  which  in  this  case   is  a   secondary    stress. 

Ductility  :     The  ductility  of  cast  iron  is  very   slight. 

MALLEAEIE  CAST   IROH 

Introduction:     Read  Articles  772  and  773  on  the  nature  and 
importance  of  malleable   cast  iron.     Malleable  cast   iron  is  white 
cast   iron,  which,   after   it  has  been  cast  into  final  form,   is  ren- 
dered malleable  by  an  annealing  process.     Malleable   cast  iron  can 
"be  cast   into   complicated  forms,   and  after   casting,    its  toughness, 
ductility,   and    strength  can  be  materially  increased.      It  is  used 
principally  for   implements,  machinery,   and  rolling   stock.     For  these 
purposes  it   is   surpassed  only  be    steel   castings  and  forgings*      It 
is  also  ussd   in  the  manufacture  of   articles  whose   form  is  too   com- 
plicated for   economical  forging. 

1,-anuf  acture  :     Read  Articles  774  to  776   inclusive.     Malleable 
cast   iron  is  made  from  foundry  pig  iron,    scrap  from  the   casting 
floor,    steel    scrap,   and  to  a  limited  extent  annealed  malleable   iron 
scrap.     The  cupola,   air  furnace,   and  openhearth  furnace  methods 
are  those   chiefly  used   in  melting  the   charge.     The  metal  must  be 


il  Engr~-8B.     Materials  of  En^r.   Construction.     Assignment  27,  page   II 

poured  ^hile  very  hot  and  as  rapidly  as  possible.     The  annealing 
process  consists  in  heating  the   castings  to  a  red  heat    (about   1300 
degrees  Fahrenheit)  for    several  days.     This  treatment   changes  the 
ccubiued  carbon  in  the  Yfhibe   oast   iron  into  graphite.     The  carbon 
does  not  precipitate   in  flakes  as  in  the   case  of  gray  cast  iron 
but  in  a  finely  divided  form  called  temper  carbon.     In  this  amor- 
phous form,  hovrever,   carbon  is  readily  oxidized,  and  in  order  to 
prevent  oxidation  the  castings  may  be  packed  in  any   inert  material 
like    sand,   or  clay.      Stronger   castings  are  made  -when  a  decarboniz- 
ing material   such  as  iron  oxide  is  used. 

Constitution:     Read  Article  777.     The  composition  of  malleable 
cast  iron  is  not  of  great  importance;   it  is  important,  however,  to 
remember  that  good  malleable  cast  iron  consists  principally  of  fer- 
rite  and  temper   carbon*     None  of  the  carbon  remains  in  the  combined 
form.      If    sand  or   clay  is  used  as  packing  material  the  heat  and 
slow  cooling  are    sufficient  to  change  the  combined  carbon  into  tem- 
per carbon,   and  the  fractured   section  of  an  annealed  casting  is 
black.     Hovrever,   if  iron  oxide   is  used  to  pack  the  castings,   it  will 
oxidize  the   carbon,   forming  CO,    so  that  the  outer    surface  will  be 
practically  pure   iron.     When   such  a  casting  is  broken  the  fracture 
has  a  white  exterior  with  a  black  center.     The  white   skin  of  carbon- 
less iron  is  rarely  over  -J-  of  an   inch  thick.     This  type  of  casting 
is  called   "black-heart."     The  outer   layer  may  be  case-hardened, 
hardened,   or  tempered. 


Civil  Engr-8B.     Maxerials  of  Engr.   Construction.     Assignment  27,  page   12 

Mechanical  properties:     Read  Article  779,  omit  Table  7.     The 
proportional   limit   of  malleable   cast   iron   is  about  20jOOO   Ib.  per 
sq«.    in.      In  compression,    since    it   is  a  ductile  material,   this 
yr.iue   is  practically  its  ujtimate    strength  for   long   slender    speci- 
mens.     In  tension  its ultimate    strength  is  about  45,000  Ib.  per    sq. 
in.      Its  average  modulus  of  elasticity   is  about  20,000,000  Ib.  per 
sq.   in.      In  tho  transverse  test  of  a  l«inch    square    specimen  its 
modulus  cf  rupture   is  about  70,OCO   Ib.  per    sq.   in.   on  a  12 -inch 
span.     Under  these   conditions  its  deflection  is  about  -|-  inch.     The 
ductility   of  malleable   cast   iron  as  measured  by  its  elongation  is 
about   7f0. 

QUESTIONS: 

1.  What  are  the  principal  uses  for  cast  iron  in  engineering 
construction? 

2.  Define  cast  iron. 

3.  Why  are  castings  not  made  directly  from  the  molten   iron  as 
it  comes  from  the  blast  furnace? 

4.  Compare  the  foundry   cupola  and  the  blastfurnace. 

5.  Is  the   cupola  or  the  air-furnace  cheaper  to  operate  and  why? 

6.  Compare  the  two  principal  methods  of  producing  cast  iron. 

7.  What  are  the  various  types  of  molds  used  in  the  production 
of  iron  castings? 

8.  What   is  chilled  iron?     What   is  it  used  for? 

9.  How  does  annealing  from  a  high  temperature    (say  over    750 
degrees  Fahrenheit)  affect   chilled  cast   iron? 


Civil  Engr-8B.     Materials  of  Engr.   Construction.     Assignment  27,  page   13 


10.  What  is   semi- steel?     What  is  it  used  for? 

11.  How  does  the  rate   of  cooling  affect  the  graphitisation  of 
cast   iron? 

12.  Discuss  the  effect  of   silicon  and  carbon  on  the  properties 
of  cast  iron. 

15.     What   is  white  cast  iron?     How  can  gray  cast   iron  be  produced? 

14 •     What  is  the  maximum  sulphur  content  allowed  in  cast  iron  by 

most    specifications?     Could  raw  materials  having  more  than 
the  allowable  amount  of   sulphur  be  used? 

15.  Name  the  principal  defects  in  iron  castings. 

16.  What   is  malleable   cast  iron?     Hov;  is  it  made? 

17-     Why  must   a  packing  material  be  used  in  the  annealing  process? 

18.      List  the    strength,   elasticity,   and  ductility  of  malleable  and 
gray  cast  iron* 


•     • 


UNIVERSITY  OF  CALIFORNIA  EXTENSION  DIVISION 
Correspondence  Courses 


s  of  Engineering  Construction 

Assignment     28 

Civil  I^igr-SB  Professor  C.T.ftiskocil 

NQN-FERROOS  METALS 

Introduction."  Iron,   copper,   aluminum,   zinc,   lead,  tin,   and 
nickel  are  the  metals  of  greatest  industrial  importance.      Iron  is  the 
most   important  metal  used  in  engineering  construction  and  for  this 
reason  it   is  usually  classed  by  itself.      The  other  metals  are 
usually  grouped  together  and  called,   as  in  the  heading  of  this 
chapter   in  the  text,  non-  ferrous  metals.     Many    secondary  metals 
such  as  cotalt,  molybdenum,  tungsten,  and  vanadium  have  no  industrial 
importance  except  as  alloying  elements. 

Copper.  -     Read  Articles  780,   781,   782  and  the  paragraph  on 
copper  on  page  522.     Copper  ores  exist  in  a  great  variety  of  forms, 
usually  as  sulphides  or  oxides.     The  principal  deposits  of  copper 
in  the     United  States  are  in  the  I^.ke  Superior  region  and  in  the 
Rocky  ilountains.      In  the   Lake  Superior  region  it   exists  as  native 
copper  ^.hile   in  the  mines  of  Arizona,  Utah,   and  Montana  it  is 
found  as  copper   sulphide  and  copper-iron  sulphide.      Copper   sulphide 
is  known  as  chalcocite  or  copper  glance,    CusS«     Most  of  the  world's 
supply  comes  from  the   copper  pyrites  or  chalcopyrite,   CuFeS,,  •    Cupr  ite 
and  malachite,   both  given  in  the  text,    are  decomposed   sulphides. 

If  the  copper  ore  does  not  contain   sulphur  the  extraction  of 
the  metal  is   simple.      Lake   copper,   for   instance  vhich  is  free  from 


Civil  Sngr-8B  assignment  28.  page  2. 

sulphur^    is  mechanically  concentrated  and  then  melted,  usually  in 
a  reverberatory  furnace,    and  the    slag    skimmed  off.     The  resulting 
metal   is  refined  by  electrolytic  or  fire  methods.      If  copper   is 
obtained  from   sulphide  orss  the  process  is  more   difficult.      It 
usually   involves  four    stages;   roasting,    smelting,    converting,    and 
refining.     The  object  of  the  roasting  is  to  drive  off  most  of  the 
sulphur   in  the  form  of  dioxide  gas  and  leave  th3  metal  in  the  form 
of  oxides*     All  of  the    sulphur   is  not  driven  off  because   it  is 
desirable  to  retain    some  to  facilitate    smarting  which  is  the  next 
step.     The  purpose  of  the    smelting  is  to  concentrate  the  ore  by 
removing  the  gangue  in  the  fom  of   slag.     The  metallic  concentrate 
is  known  as  matte  vhich  is  essentially  metallic    sulphides  of 
copper,   iron,   and  any  other  metals  originally  present  in  the  ore. 
Smelting  is  done   in  a  blast  furnace  or   in  a  reverberatory  furnace, 
the   latter  furnishing  a  richer  matte.     The  matte  is  purified  in  a 
Bessemer   converter.     The  air  blown  through  the  molten  metal 
eliminates  the    sulphur  and  forms  -That  is  knovrn  as  blister  copper. 
Blister   copper  is  refined  by  fire   and  electrolytic  methods.  The 
electrolytic  method   is  used  to  produce  the   finer  grades  of  copper, 
.jaodes  of  blister  copper  are  placed  in  a   strongly  acid  copper 
sulphate    solution.      Cuthod.es  of  very  pure   copper  are  used  and 
pure  copper  from  the   anodes  is  deposited  on  them  -rhen  an  electric 
current   is  passed  through  the   circuit.      Impurities  are   insoluble 
in  the  electrolyte,   and  fall  to  the  bottom  in  the    slices.     T.hen 
these   include  trie   precious  metals  they   can  bo  recovered  from  the 
re  siduc. 


Civil  £ngr.~8E  Assignment  23.  page   3. 

% 

The   two  principal  classes  of  copper   are  electrolytic   copper, 
v/hich  is  obtained  by  the  method  just   described;    and  Lake  copper, 
v;hich  is  obtained  from  ores  mined  in  the   Lake    Superior  region. 

Copper   is  a  malleable,   ductile  metal  having  high  electric 
conductivity   and  great  resistance  to  atmospheric  corrosion.      Copper 
does  not  cast  veil,   most   copper  products  being  therefore  dravm  or 
rolled.     Ilechanical  working,    such  as  drawing  has  a  greater  effect 
on  the  physical  properties  of   copper  than   it  does  on   steel.     Hot 
rolled  copper  has  an  ultimate  tensile    strength  of  30,000   Ib.  per 
sq.    in.,   and  an  elastic  limit  of  7,000   Ib.   per    sq.    in.,  -vvith  an 
elongation  of   5C^.      Cast  copper  has  approximately  the    same    strength 
but   its  elongation  is  much   less,  being  about  7/b.      Cold  drawn 
copper    in  the  form  of  wire,  has  an  ultinate  tensile    strength  of 
50,000    Ib.   per    sq.    in.,   an  elastic   limit  of  30.000   Ib.   per    sq.    in* 
with  an  elongation  of  about  2^.      Its  modulus  of  elasticity  is 
about   15,000,000   Ib,  per    sq.    in. 

The  uses  of  copper   are  well    stated  in  Article  782. 

Zinc.-     Eead  Articles  783,734,   765  and  the  Daragraph  on 
zinc  on  page   523. 

Zinc    sulphide,  which  is  known  as  zinc  blendq    (ZnS)>    is  the 
principal    source  of   zinc.      The  deposits  of  zinc   carbonate,   called 
zinc    spar  or   calamine    (ZnCO^),   are  being  rapidly  exhausted.     2.inc 
silicate    (Zn^SiOS-  rL-,0)      is  of   lesser   importance.     The  chief  deposits 

(••  rr         C» 

in  the  United   States  are   in  Wisconsin.,   .lisscuri  and  NOT  Jersey. 


Civil  Engr.-8B  Assignment  28.  page  4. 

Zinc   ores  are  roasted  to  convert  them  into  the   oxides,  -rhich 
are  then  mixed  with  carbon  and  heated.     The   carbon  combines  with 
the  oxygen  of  the   oxide  and  pure   zinc   is  volatilized.      The   zinc 
vapor   is  condensed  and  poured  into  ingots.      In  this  form  it  is 
known  to  the  trade   as   spelter.      Spelter   is  rcmelted  and  rolled 
into    sheet   sine. 

Since   zinc   is  rarely  usod  as  a   stress-carrying  member  of 

•    -     -    i 
a  machine  or    structure  its  tensile    strength  is  not  important. 

The  fact  that   it  casts  well  and  has  a  high  resistance  to  atmospheric 
corrosion  makes  it    adaptable  for   a  protective  coating  for  iron  and 
steel.    ,<hen   so   coated  the  materials  are   known  as  galvanized  iron. 
Zinc   is  put  on  in   several  -//ays.     The  metal  may  be  dipped  in  molten 
spelter   or  the   zinc  may  be   deposited  electrolytically,   or  the  coat- 
ing may  be  formed  by  the  condensation  of  volatilized  zinc  dust, 
as  the  result  of  a  process  known  as  stierardizing.     Zinc   is  used 
as  the  negative  element  in  nearly  all  primary  batteries.     Zinc 
dust  and  pigments,    such  as  zinc   oxide   and   lithopono,   arc   commercial 
forms  of   zinc. 

Aluminum*  -     Read  ^ticies  786,787,788,    and  the  paragraph  on 


aluminum  on  page 

In   5)  ite   of   its  abundance,   aluminum  is  never  found  in  the  free 
state,    and   it   is   only    since   1886  that   it  has  been  produced  on  a 
commercial    scale.     Bauxite    is  -a  hydrated  oxide    (^IpOg.SHgO).    It 
is  the  principal    source  of  aluminum.     Aluminum  oxide   is  called 


Civil  Engr-8B  Assignment  28  page  5 


fJ^EH1!  ^-12°3>  which  is  a"  essential  ingredient  of  clays.     The 
bauxite    is  converted   into  alumina  which  is  dissolved    in  molten 
cryolite    (AlPj.SHaF)   from  ^vhich  mixture  the  metallic   aluminum 
is   separated   by  electrolysis. 

Aluminum  is  very  light  but  has  considerable   strength;   it 
is  malleable,   non-corrosive,    and  ductile,   and   it  has  high  electric 
conductivity.      It  is  made   into  various  shapes  by  rolling,   pressing, 
drawing,    and  casting.     Because  of  its   low  electric  resistance 
and   lightness   it  is  v/ell  adapted  for  use   on  long-span  transmission 
lines.      It   is   also  used  for  bus-bars  and  rode   in  power  houses. 
aside  from  the  uses  stated   in  Article  738  it  is  used  to  quiet  molten 
metal  before  casting,   for   thermit,  which  is  used   in  welding  (pre*- 
viously  referred  to),   and   in  the  form  of  powdered  aluminum,   as 
a  paint  pigment  and   in  explosives. 

Cast  aluminum  has  a  tensile   strength  of  about  13,000  Ib. 
per  sq«    in.   rith  an  elastic   limit  of  9,000  Ib.    per  sq.    in.   and 
elongation  of  20%.     When  drawn  its  tensile   strength  increases 
to  30,000  Ib.    per    sq.    in.    and   its  elastic   limit  to  about  20,000 
Ib.    per   sc.    in.   while   its  ductility  is  decreased. 

Lead.-  Read  Article   789  and  the   paragraph  on  lead   on  page 
522.     Galena   (?bS)   is  the  only  important  ore   of  lead.     The  United 
States   le?^s   in  the  production  of  lead.      The   essential   steps   in  the 
extraction  of  lead   from  its   ores   are  roasting  and   smelting.      There 
are   other  secondary  operations,      ^jaong  these   is  the  desilverizing 


Civil  Bngr-8B  Assignment   28 


page  6 


the  lea 4,  if  there  are  sufficient  amounts  cf  silver  present.   The 
properties  of  lead  which  are  of  most  importance  are  its  malleability, 
plasticity,  and  resistance  to  atmospheric  ccrrogim.   Its  chief 
uses  ars  listed  in  the  text  but  an  important  use  is  omitted,  namely, 
its  use  in  the  manufacture  of  storage  battery  plates. 

Tin.-  Read  article  790.   The  ores  of  tin,  their  occurence, 
and  the  method  used  in  extraction  of  the  metal  are  clearly  described 
in  the  text.   The  uses  of  them  are  also  given.   Its  high  degree 
of  malleability  and  its  resistance  to  atmospheric  corrosion  mc.ke 
it  of  commercial  importance.   Tin  plate  is  thin  sheet  steel  (a  soft 
lo*v-carbon  steel  is  used)  covered  r/ith  a  coating  of  pure  tin. 

Nickel.-  Read  /article  791.   Nickel  is  highly  resistant  to 
atmospheric  corrosion.   It  has  a  silvery  appearance  and  is  used  to 
plate  iron,  steel  and  other  metals.   Pure  nickel  \voulc  be  an 
excellent  structural  material,  since  its  properties  ?re  similar  to 
those  of  medium  carbon  steel,  Taut  it  is  too  expensive.   Alloying 
nickel  with  copper  to  form  v/hat  is  known  as  monel  metal  makes  the 
product  somerrhat  cheaper,   iionel  metal  contains  about  67f0  nickel, 
28%  copper  and  b%  other  metals,  among  which  are  iron,  silicon, 
manganese,  and  carbon.   Its  values  for  tensile  and  compressive 
strength,  and  its  uses  are  listed  in  the  te:rt.   Its  strength  compares 
well  with  that  of  steel,  and  this  fact  coupled  with  its  great  re- 
sistance to  corrosion  and  the  action  of  sea  vater,  make  it  a  very 
desirable  naterir.l. 


Civil  Engr.-8B.         Assignment  28.    .          page  7o 

NON-FERROUS  ALLOYS 

Introduction.-  Lietais  are  alloyed  to  change  their  properties. 
Undesirable  properties  can  "be  decreased  and  desiraole  properties 
G'-.n  be  increased  through  the  use  of  alleys.  Alloys  may  be  harder, 
tougher,  more  ductile, and  may  have  better  casting  qualities,  or 
greater  tensile  strength  than  any  of  the  constituent  elements, 
Furthermore  the  cost  of  production  can  Le  lessened. 

Brasses. -  Read  Article  722  and  793.  An  alloy  of  copper  and 
zinc  is  knov/n  as  brass-,   la  special  brasses  a  third  metal  is 
added*  Brass  and  bronze,  an  a] loy  of  copper  and  tin,  which  vill 
be  discussed  later,  form  the  commonest  yet  the  .-lost  important 
of  the  non-ferrous  alloys.   They  can  be  cast  into  the  desired 
shapes  or  rolled  into  sheets  c.nd  rods.  Brass  can  be  draivn  into 
-.vire,  while  bronze  is  usually  cast  into  shape.   In  general,  brass 
hrs  less  strength  than  bronze.  Brasses  and  bronzes  are  not  so 
strong  c.s  iron  and  steel,  but  they  are  less  subject  to  corrosion, 
and  are  used  ivhere  long  exposure  to  moisture  is  necessary,  as  in 
pumps,  and  for  hydraulic  fittings.   Br<.'.ss  is  also  used  as  a  bearing 
metal  for  steel  shafts.   Brass  is  relatively  expensive,  being  aboat 
seven  tirr.es  more  costly  than  steel. 

The  proportions  of  copper  and  zinc,  in  the  manufacture  of 
brass,  may  be  varied  ever  vide  limits.   I he  figure  on  page  741 
is  quite  complex.   It  is  sufficient  to  remember  that  ~hat  is 
knov;n  as  standard  brass  (about  2  parts  copper  to  1  part  zinc) 


Civil  Engr.-8B.  Assignment  28.         .  page   8. 

is  most  commonly  used   of  all  tne  brasses.      Jn  the  cast  form  its 
ultimate  tensile   strength  is  about  50,000  Ib.    per   sq.    in.    and  the 
elongation  is   about  30%,  with  a  modulus   of  elasticity  of  about 
13,000,000  Ib.    per  54.    in.    Standard   brass  is  more  resistant  to 
corrosion  than  brasses  which  contain  less  copper.      Munz  metal, 
60$  copper  to  40%  zinc,    is  not  used  as  much  as   formerly. 

Manganese  bronze   is  the  nost  important  of  the  special 
brasses.      The  manganese   is  added  to  the  brass  in  the  form  of 
ferro-nanganese  as  a  deoxidizer.      The  effect  is  to  strengthen 
and  harden  the  alloy.        Usually  there  are   only  traces  of  manganese 
left   in  the  finished  product  since  most  of  it  is  fluxed   off.      Its 
strength  and  toughness  are  equal  to  those   of  steel;   besides,    it   is 
readily  cast  and   is  highly  resistant  to  corrosion  by  sea  wtter, 
alkali  vater,   and  r/eak  acids. 

Bronze.-  Read  ^irticles  794  and  795.      ^J.loys  of  copper  and 
tin  have   oeen  known  since  prehistoric   times.      Commercial  bronzes 
usually  contain  more  than  80^o  copper.        LJachinery  bronze  generally 
contains     about  85$£  copper.      It  is  used  as  a  bearing  inet^l,  for 
cut   gears,   bushings,    stuffing  boxes,   and  plumbing  fixtures.      Gun 
netal  and   bell  metal  are    uhe  more   important   of  the  simple  bronzes. 
Machinery  bronzas,    in  the  cast  form,   has  a  tensile   strength  of 
about  30,000  Ib.    per   so.    in.   with  an  elongation  of  10/i  and   a 
modulus  of  elasticity  of  15,000,000  Ib.    per   sq.    in. 


Civil  Engr.-8B         ^ssigrnnent  28-  pc.ge  0". 

The  special  bronzes,  copper -tin- zinc  alloys,  are  the  most 
valuable  and  in  most  general  use.   Machinery  bronze  referred  to 
sbotf-e  is  usually  made  with  some  zinc.   The  addition  of  phosphorus 
to  any  bronze  produces  a  mcrked  increase  in  its  strength  and 
ductility,  '.-Then  of  proper  composition,  phosphorus -bronze  can  be 

dr-^wn  cold,  forged,  rolled,  and  cast.   It  is  used  where  high 
strength  '.nd  resistance  to  corrosion  are  controlling  factors, 
phosphorus,  as  in  the  case  of  manganese,  is  a  strong  deoxidizing 
agent.   Only  small  amounts  of  residual  phosphorus  remain  in  the 
finished  metal. 

The  three -metal  alloys  (copper-zinc-tin)  can  be  m^de  so 
that  they  have  high  strength  and  considerable  ductility.   The 
final  properties  of  the  alloy  depend  upon  the  mechanical  treatment, 
such  as  rolling  and  drawing,  as  ^ell  as  upon  composition  and 
foundry  practice,  which  Y/ould  include  temperature  of  pouring. 
Cold  v/orking,  driving,  or  rolling  generally  raises  the  elastic 
limit  uid  ultimate  strength  of  these  alloys. 

Season  crack:.ng  of  brass  and  bronze.-  Read  Articles  796, 
797,  and  798.   Sound  metal  in  the  form  of  sheets,  rods,  and  tubes 
vili  often  develop  crocks  under  service  or  even  while  in  storage. 
Crocking  of  this  kind  is  also  produced  by  corrosion  and  sudden 
changes  in  temperature.   It  is  called  season  crocking  anc  sometimes 
corrosion  cracking. 

Season  cracking  may  be  prevented  by  annealing  ana  springing. 


Civil  Engr. -SB-       ^ssigniaent  28.     .          page  io. 

Springing  is  described  in  the  text.  Annealing  must  be  carefully 
done  so  us  not  to  weaken  the  metal,  especially  if  it  is  to  be 
used  for  springs.   The  concentration  of  stresses  .at  the  base  of 
scratches  and  corrosion  pits  can  be  prevented  by  polishing  the 
metal.   These  localized  stresses  are  a  source  of  season  crack-ing. 
The  chief  cause  of  season  cracking  is  the  internal  stresses  set  up 
in  the  metal  by  cold  "working. 

The  presence  of  internal  stresses,  besides  subjecting  the 
metal  to  possible  season  cracking,  causes  distortion,  if  part  of 
the  stresses  are  relieved  by  the  removal  of  some  of  the  metal,  by 
boring,  or  by  the  cutting  of  keyivays.  This  condition  exists  also 
in  the  c^ss  of  cole1  rolled  steel  shafting. 

Alloys  of  aluminum.-  Read  Articles  799  to  803  inclusive. 
The  Uoes  of  thsse  alloys  are  given  in  ^tide  799.  The  principal 
alloys  are  aluminum  bronze,  aluminum-zinc  alloys,  and  duralumin. 

^iuminum  bronze  contains  about  90^  copper  and  10^'  aluminum. 
Since  it  contains  no  tin  it  is  really  not  a  bronze.  Aluminum  bronze 
is  an  alloy  of  high  strength  and  ~ood  ductility. 

Duralumin  contains  about  9b%  aluminum  with  copper,  magnesium 
and  manganese  as  indicated  in  the  text.   On  account  of  the  large 
percentage  of  aluminum,  it  is  very  light  in  weight,  about  175  Ib. 
per  ctu  ft. ,  as  compared  with  480  Ib.  per  cu.  ft.  for  rolled 
steel.   It  is  used  for  drawing  and  rolling.   Similar  alloys  are 
sold  under  various  trade  names  but  their  properties  are  similar  to 


Civil  &npr.-8B  ^jssignment  23. 


tliose   of  duralumin.      These   alloys   have  made  the  large   dirigibles 
(air   ships   of  the   Zeppelin  type)   possible.      In  their  constr  action 
the   strength  of   stesi  with  the    lightness   of  aluminum  is  necessary. 

Bearing  metals.-     Read  ^jrtidsfi  804  to  808   inclusive. 
Satisfactory  bearing  metals  must  have  sufficient  compressive 
strength  to  withstand  the  bearing  pressure,  and  they  must  develop 
little  friction  \/hen  the  surfaces  coine  into  actual  contact,   as 
*vhen  a  shaft  stops  rotating.     j.±  Yrell  oiled  bearing  in  notion  vill 
hr.ve   little  friction  irrespective   of  the  kind   of  metal  used  because 
of  the   oil  film  on  the  moving  surfaces  but  when  motion  stops  the 
oil  film  is  broken  and  the  metal  surfaces  come  into  contact  and 
anti-friction  metal  is  then  necessary.      Host  shafting  and   sliding 
p^rts   of  machines  are  made   of  steel;  bearings  cannot  be  ma.de  of 
steel  because  steel  surfaces  ruboing  together  v;ould  cut  and  tear 
each  other*      Cast   iron,  bronze,  brass,  Babbit  metal  and   other  anti- 
friction matals  are  used.     Lead   is  too  soft  for  a  bearing  metal. 
;Ls   indicated    in  Table   4  on  page  757,   alloys   of  lead  and   antimony 
(used  to  hirden  the   lead)  are  the   softest  bearing  metals. 

Good  bearing  metals  have  a  crystalline   structure  composed 
of  tvjo  types   of  crystal,    soft  and  hard.      The   hard   crystals  carry 
the   load    r-nc   resist  wear.      The   soft  crystals  yield   and  allow  the 
harder  crystals  to  adjust  themselves  to  any  irregularities  in  the 
moving  surface,   and   also  wear  out  belcr.v  the   actual  surface   of  the 
bearing,   thus  forming  a  surface  which  readily  holds  the   lubricant. 

The  soft  bearing  metals,   of  which  Babbitt  metal   is  the  bast 
c^wnift     ^y^   o    *+.  rM  reetlv  in  clr.ce    and   usually  require  no  machining 


Civil  Engr.-8B  Assignment  28.  page  12' 


QUESTIONS 

1.        Name  the  metals   of   greatest   industrial   importance.      HOT;  :.re 
they  generally  classified? 


2.   V.hTt  are  the  principal  copper  bearing  ores? 

3o   HOY;  is  metallic  copper  obtained  from  the  sulphide  ores? 

That  are  the  appro::  irac.te  tensile  strength  and  elastic  limit 
of  hot  rolled  and  cold  drawn  copper? 

5.  Vvhat  is  galvanized  iron?  HOW  is  it  made? 

6.  Why  is  aluminum  particularly  adapted  for  use  in  long-span 
transmission  lines? 

7o  What  are  the  principal  uses  for  lead  e.nd  tin? 

8.  What  is  monel  metal?  uhat  are  its  chief  characteristics? 

9.  What  is  brass? 

10.  What  is  bronze? 

11.  Row  does  manganese  affect  the  properties  of  brass? 

12.  Why  is  brass  that  has  been  i/orked  cold  more  liable  to  season 
cracking  than  orass  that  has  been  worked  while  hot? 

13.  What  precautions  can  be  taken  to  prevent  season  cracking? 

14.  What  are  the  requirements  for  a  good  bearing  metal? 

15.  Name  the  different  bearing  metals. 

16*   What  ?.re  the  advantages  of  bronze  over  BabDitt  metal  as  a 
bearing  metal? 

17.  Why  would  bronze  be  preferrable  to  cast  iron  for  a  bearing 
for  a  steel  shaft? 


UNIVERSITY  OF  CALIFORNIA  EXIEfc'Sia*   DIVISION 
Correspondence     Courses 

Materials  of  Engineering  Construction 
Civil  Engr-8B  Assignment  29  Prof.   C.  T.  Wiskocil 

FATIGUE  OF  METALS 

Introduction:     Read  Article  821.     Fatigue  results  from  the 
inability  of  a  metal  to  carry  repeated  loading  rrhich  does  not 
stress  it  in  excess  of  its  elastic  limit.     The  fatigue    strength 
or  endurance   limit,   as  it  is  often  called,    seems  to  be  a  definite 
unit   stress,   as  isrell  defined  a  property  as  the  ultimate  tensile 
strength. 

Vihen  metal  parts  of  machines  or   structures  are    subjected  to 
static  or   impact   stresses  they  either  withstand  the   load  or  they 
fail,  that  is,  they  are  actually  ruptured  or  else  rendered  un- 
usable  by  distortion  or  deformation.     The  maximum  loading  under 
these  conditions  can  be  quite  accurately  estimated  by  the  results 
of  relatively   simple  tests;   but  under  conditions  of  repeated   stress 
such  as  occur  vhen  a  piece  of  metal  carries  a  load  perhaps  a  mil- 
lion times  and  then    suddenly  ruptures,  the  maximum   safe   load  is 
not    so  easily  determined.     The   load,  up  to  the  time  of  actual 
fracture,  apparently  does  no\  damage.     This  is  the  characteristic 
feature  of  the  fatigue  of  metals. 

In  the  design   of  metal  bridges  and  buildings  the   loads  are 
kept  v/ithin  the  elastic   limit  and   localized    stresses  do  not  cause 
static  failure.      It  has  been  estimated  that  the    stresses  in  mem- 
bers of  an  ordinary  railway  bridge  are  repeated   less  than  tiro 


Oivil  Eng:*-8B  Assignment  29  Page  2 

million  times  during  a  period  of  fifty  years.      In  these    structures 
the  unit    stresses  are  not  large  and  they  are  repeated  a  relatively 
small  number  of  times.     Fatigue,  therefore,   is  not  important  and 
the  criterion  of   static   strength  governs  the  design. 

In  the   case  of  machine  parts,  however,  fatigue   is  a  major 
factor.     The  crankshaft  of  an  airplane  motor  is  subjected  to  about 
twenty  million  reversals  of   stress  in   less  than  200  hours  of  fly- 
ing.    The   stresses  are  relatively  high   since  the  motor  is  constant- 
ly operated  at  nearly  maximum  power.     The   stresses  in  the   shaft 
of  a   steam  turbine,   if  operated  continuously  for  ten  years,  would 
"be  reversed  about    sixteen  billion  times.     Fatigue,  therefore,  must 
te  considered  in  the  design  of  machine  and  automobile  parts  such 
as  crankshafts,  piston  rods,  connecting  rods,   crankpins,    springs 
and  axles. 

If  a  loud  is  put  upon  a  piece  of   steel  and  then  removed,  the 
metal   is  said  to  have  been   subjected  to  a  cycle  of   stress.      Since 
steel  isAhomogenous,  the  minute  constituent  particles  move  on  one 
another  during  a  cycle  of    stress.     For  a   single  cycle,   if  the 
maximum  stress  is  within  the  elastic   limit,  the  heat  generated  by 
the  microscopic  movement   is  not  appreciable  but   if  the    stress 
cycle   is  repeated  the  rise   in  temperature  of  the  metal  is  noticeable 
The  friction,  7/hich  presumably  causes  this  heat,  finally  weakens 
some  minute  element  to    such  an  extent  that   it  actually  ruptures. 
This  failure   of    some  minute  element  undoubtedly  forms  a  concentrated 


Civil  Engr-8B  Assignment  29  Page  3 

area  of  high   stress  and  from  this  nucleus  the  fracture    spreads  to 
adjacent  crystals  and  the  progressive   increase   in  the   size  of  the 
original  cleavage  plane  or  crack  causes  the  failure  of  the  entire 
member.     High  localized   stress  is  also  formed  at  the  base  of   sur- 
face   scratches  or  at  the  root  of  a   screw-thread  or  at  a  minute 
blow-hole  or    similar   internal  defect.     These  are  typical  conditions 
which  lead  to  failure  from  fatigue.      It   should  be  noted  too,   that 
failure  of  machine  parts  is  often  the  result  of  a  combination  of 
fatigue  and  damage  by  occasional  overstrain. 

The  relative  movement  of  the  elements  of  minute    steel  crystals, 
v.'hen  under    stress,  was  first  observed  by  Evring  and  Rosenhain  in 
1899 r     The  movement  became  evident  as  dark  parallel   lines  across 
the  faces  of  individual  crystal  grains  as  they  were  viewed  under 
the  microscope  when  illuminated  by  oblique   lighting.     The  accomp- 
anying diagramatic  cross- sectional    sketch    shows  how  the   light  would 
cast    sh.".dovs  T'hich  vould  appear   as  parallel  lines,    called   slip- 
lines,  v.-hen  viewed  from  the  direction  indicated.     Four  years  later 
Eving  and  Humphrey    (as  will  be  described  under  the    subject  of   slip- 
lines)   observed  that  the    slip-lines  developed  in    steel  by    subjecting 
Direction  of   observationL,  ^Direction  of   light 


*MX         *j 

Polished    surface  ^-J*~JF 

of 


Crystal  boundaries  not    shown 


Civil  Engr-8B  Assignment  2-9  Page  4 

it  to  repeated  cycles  of  stress,  would  develop  into  microscopic 
cracks  which  in  turn  vrould  spread  and  cause  ultimate  failure  of 
the  entire  member. 

Crystallization  of   steel:      Study  Article   822.     \flien   steel  is 
subjected  to  a   sufficient  number  of  reversals  of   stress,   even 
though  the    stress  is  -within  the  elastic   limit,  the  induced  fatigue 
makes  it   liable  to   sudden  rupture.     With  this  type  of  failure  there 
is  no  preliminary  deformation   (read  third  paragraph  on  page  779) 
and  the  fracture  is  crystalline  as  in  the  case  of  cast  iron  or  any 
brittle  metal.     The  appearance  of  the  break  and  the  characteristic 
suddenness  with  -which  failure  occurs  gave  rise  to  the  theory  of 
the  cold  crystallization  of   steel  -  and  it  is  still  popularly  be- 
lieved that  fatigued   steel  becomes  crystallized.     This  misconcep- 
tion is  fostered  by  the  fact  that   sudden  failures  display  the 
crystalline   structure  of  a  metal,  which  in  the  case  of  gradual 
failure  as  in  a   static  test,   is  disguised  by  the  elongation  and 
necking  of  the  piece  due  to  its  ductility.     Therefore,  when  fatigue 
failure   occurs  in  a  ductile  metal,    such  as  steel,   it  is  argued  that 
since   it  brote suddenly  with  a  crystalline  fracture  the  material  be- 
came crystallized,   and  hence  was  made  brittle,  by  the   induced 
fatigue . 

Sudden  failure  is  attributed  to  brittleness  but  it  is  possible 
to  produce  a  crystalline  fracture   in  a  piece  of  mild   steel  of  known 
ductility  by  cutting  or    sawing  a  rod     .part  way  through  and  then 
completely  breaking  it  by   a   single  blow  with  a  hammer.     The 


. 


Civil  Engr-8E  Assignment  29  Page   5 

resultant  fracture  will  be   granular  because  the  grains  haye  had 
no  time  to  elongate  and  disguise  the  crystalline   structure-     The 
fracture  resembles  that  c.f  brittle  metals  which  fail   suddenly  and 
•without  apparent  warning. 

The  popular   conception  of  fatigue  being  caused  by  vibration 
and  repeated   stress  under   conditions  of   continuous  service  is  cor- 
rect,  although  the  deterioration  is  not  produced  as  easily  as  is 
beleived;  but  the  phenomenon  implied  by   the  term  crystallization 
does  not  exist.     The  crystallization  of   steel  occurs  when  it^ 
solidifies  from  the  liquid   state,  therefore,  the  metal  in  the   solid 
state   is  inherently  cyrstalline.     The  crystalline    structure  of 
steel  has  been  repeatedly  referred  to;    see  illustrations  such  as 
those  on  pages  628,   632  and  637  in  the  text.     Change  in  crystal 
size  or  recry stallization  can  nevertheless  be  produced  by  thermal 
treatment.      (The   increase   in  grain   size  by  overheating  without 
proper   annealing  has  been  discussed  under  the    subject  of  Steel). 
The  misconception  arises  in  the  meaning  of  the  term  crystallization 
because  the   laymen  who   still  adhere  to  the  theory  of  cold  crystal- 
lization believe  that  the  fatigue  of    steel,  which  occurs  under   in- 
fluence  of    shocks  and  vibration,   produces  gradual  enlargement  of 
the   crystals  and  corresponding  brittleness. 

Two  reports  on  failures     attributed  to  cold  crystallization 
because   of  the   large   crystals  appearing  in  the  fracture  were   later 
discredited  when   it  was  found  that  the  ruptured  members  had  at  one 
time  been  heated  -  undoubtedly  overheated.     These  reports  appeared 


Civil  Engr-8B  Assignment  29  Page   6 

in  the  Engineering  Record  of  December   13,   1913  as  an  editorial 
note,   and   in  the  Report  made  on  Division  Street  Bridge  Failure   in 
Spokane,  Engineering  Record,  Vol.73,  page  29   (January  1,   1916), 
and  also  an  editorial  on  the    saae    subject  in  the  following  issue 
(January   8,    1916).      It  will  be  recalled  from  previous  discussions 
on  this  subject  that  fresh  fractures  of  overheated   steel    show 
large  brilliant  facets  which  are  a  criterion  of  the  actual   struc- 
ture.    The  overheating  causes  an  increase  in  the    size  of  the 
crystals  and  a  decrease  in  the   strength  and  ductility  of  the  metal. 
The   large  facets  in  a  fatigue  failure  are  formed  -while  the  deterio- 
ration is  in  progress  by  a  continuous  cleavage  plane  extending 
through  two  or  more  adjacent  crystals  which  tends  to  exaggerate 
the  apparent    size  of  the  crystals  on  the   surface  of  the  break. 
But  according  to  Deseh  a  microscopic  examination  of  the  metal  be- 
hind a  fatigue  fracture    shows  no  change  in  its  structure  or   in- 
crease  in    size  of  the   individual  crystals. 

While  crystal    size  can  be   increased  by  thermal  treatment 
there    is  no  evidence  that   crystal  growth  of    steel  can  be  produced 
by    strain  at  atmospheric  temperatures.     This   statement  is  true 
for  nearly  all  metals.     Lead  is  an  exception,  however,   inasmuch  as 
overstrain  by  plastic  deformation  results  in  a  decided  crystalline 
grovrbh  in  this  metal  even  at  atmospheric  temperature s« 

The  popular  idea  of  cold  crystallization  of   steel   still  exists, 
&***.  in   spite   of  the  fact  that   the  true  cause   of  fatigue,  which 
will  be   discussed  later,  was  discovered  in  1903.     The    statement 


:•-  -..  •-  ••_  •=    -.-'..     .    ••'..•  •-'-.    '• 


Civil  Engr-83  Assignment  29  '  Page  7 

is  often  heard  that  the  axles  of  Ford  automobiles  crystallize   in 
service  due  to  continued  vibration.     This  is  not  to  be  wondered 
at   since  as  late  as  1915  many  engineers  still  believed  in  cold 
crystallization.     In  THE  LIFE  OF  IRON  AND  STEEL  STRUCTURES  by 
Frank?/.    Skinner    (consulting  engineer,  Nev  York)  Paper  No.   107  of 
the   International  Engineering  Congress,   IS 15,   San  Francisco, 
California,  Volucne  on  Materials  of  Engineering  Construction,  page 
442,  we  find  the  following   statement  on  the    subject  of  crystalli- 
zation:    "That  iron  and   steel  are  often  found  after   severe   service 
with  a  damaged  crystalline   structure,   is  undoubted,  but  it  is  many 
times  a  moot  question  i/hether  this  condition  vras  developed  in   ser- 
vice, or   during  the  original  manufacture  of  the  metal»u     In  the 
discussion  of  the    same  paper,  however,  Edgar  Marburg  cautioned 
against  the  perpetuation  of  the  erroneous  cold  crystallization 
theory. 

Slip -lines:      Study  Article  823;    it  is  very  important.     Marked 
progress  in  the    study  of  the  fatigue  of  metals  ?ras  made  by  the 
English    scientists,  Swing  and  Humphrey.     Their  investigations  are 
remarkable  for  the  accuracy   of  observation  and  the   ingenious 
check  on  their  theories-      In  1903  the  paper   "The  Fracture  of  Metals 
under  Repeated  Alternation  of  Stress"  explained  their  experiments 
and  proved  that  the  primary  cause  of  fatigue  failure   in  a  ductile 
metal    (steel)  was  the  result  of   localized  deformation  which  was 
evident  under  microscopic  observation  as  a   sliding  of  the  crystal 
elements  on  each  other   and  the  final  rupture  of  individual  crystals. 


: 


Civil  Sngr-CB  Assignment  29  page  8 

Their  test  pieces  which  could  be    subjected  to  any  desired  bending 
moment,  ^ere    short  rods  supported  in  a  revolving  mandrel.     The 
region  of  greatest   stress  was  polished  and  etched  beforehand,   for 
the  purpose  of  observation  under  the  microscope  before  and  after 
a  definite  number  of  revolutions,  which  produced  reversals  of 
stress  in  the  rods.     These  observations  'were  repeated  at  frequent 
intervals.     The  formation  of  and  development  of   slip-bands  or 
slip -lines,   are  clearly  described  in  the  text. 

The    slip-bands,  which  were  first  observed  by  Ewing  and 
Rosenhain  on  the  polished   surface  of  overstrained  metal,  mark  the 
boundaries  or  cleavage  planes  between  the  elements  of  the  indi~ 
vidual  crystal  as  its  resistance   is  weakened  by  repeated  reversal 
of   stress,   and  it  draws  out,  the  elements  slipping  on  each  other 
like  a  pack  of  cards.     The  formation  of   slip-bands  does  not  involve 
any  change  in  the   crystal  arrangement  or  any  increase   in  crystal 
size.      In  normal  metal  the  actual  failure  or  break  passes  through 
the  crystal. 

From  these  phenomena  and  the  observations  of  Beilby  which 
lead  to  the  discovery   of  the  nature  of  the    surface  produced  on 
metals  by  polishing,  we  get  a   satisfactory  explanation  of  the  action 
oi1  metals  under    stress.     The  mechanical  movement   in  polishing 
causes  the  extreme  outer   layer  of  metal  to  flow  thus  forming  a   skin 
possibly  hundreds  of  molecules  in  thickness.      Similar  but  much 
thinner  films  of  amorphous  metal  are  formed  on  the   surface  of  intra- 
crystalline   cleavage  planes  which  become   so   strongly  cemented  by 


Civil  Engr-8B  Assignment  29  Page   9 

the  hardening  of  the  film,   after   a  period  of  temporary  mobility, 
that  planes  where  no    slip  has  occurred  are  weaker   in  comparison. 
In  this  manner  the  weak  portions  have  their    strength  increased 
and  a  greater    stress  is  necessary  to  effect   slip  or  deformation 
than  was  first  required.     This  process  results  in  the   increase   in 
elastic    strength  of  the  material  when  the  metal  has  been  over- 
strained.     It  has  been   shown  that  there  is  slight  movement  along 
the   inter crystal line    surfaces  but  it  appears  that  the  actual  do- 
ne sion  between  adjacent  crystals  is  much   stronger  than  that  be- 
tween different   layers  of  the    same  crystal.     This  explains  the 
high  elastic   limit  given  to  drawn  wire  by  the  overstraining  of  the 
metal  as  it  is  drawn  through  the  die. 

In  the  action  of  metal  under  reversals  of   stress  the    slip 
between  different  layers  of  a  crystal  is  continuously  reversed  in 
direction  and  at   such  frequent  intervals  that  the  mobile  amorphous 
film  eventually    solidifies  without   cementing  the   adjacent   layers- 
A  microscopic  crack  develops  which  weakens  that  particular   crystal, 
and  additional   stress  is  thereby   -transferred  to  adjacent  crystals, 
which  undergo    slip  and  gradual  deterioration  in  the    same  way. 
Final  rupture  occurs  at  a  unit   stress  below  the  primitive  elastic 

limit* 

Experiments  on  fatigue:  Read  Article  824.  The  first  study 
of  fatigue  and  its  effect  on  iron  and  steel  was  undoubtedly  made 
by  Fairbairn  who  published  his  results  in  1864.  His  experiments 
are  referred  to  in  the  text.  In  1870  Wohler  presented  his  data, 


••• 


Civil  Engr-8B  Assignment  29  '  Page   10 

which  were  talisn  during  an  investigation  extending  over  a  period 
of   12  years.     Wohler!s  conclusions  are   substantially  in  accord 
with  the   latest  experimental  information.     Spangenberg  substantiated 
Wohier's  conclusions  in  1874,  while  the  famous  Baushinger  published 
the  results  of  his  work  twelve  years  later.     The  first  information 
on  the  true  action  or  mechanism  involved  in  fatigue  failure  was 
not   knovna  until  1903  when  Ewing  and  Humphrey  reported  their   study 
of  metals  under  repeated   stress.     Fatigue  tests  of  metals  have  also 
been  made  at  the  Watertovm  Arsenal.      Important  conclusions  were 
reached  in  an  investigation  of  the  fatigue  of  metals  conducted  by 
The  Engineering  Experiment  Station,  University  of  Illinois,   in  co- 
operation with  The  National  Research  Council,  The  Engineering 
Foundation,   and  The  General  Electric  Company.     The  results  are  re- 
ported in  Bulletin  No.   124  of  the  University  of  Illinois  Engineering 
Experiment  Station,  by  H.  F.  Moore  and  J«  B«    Kbmmers  (Dated  October 
1921). 

The  most  important  conclusion  in  the   Illinois  tests  was  the 
confirmation  of  the  existence  of  a  limiting   stress  (see  paragraph 
4,   Figures  1  and  2,   and  the  discussion  relating  thereto  on  page 
773)  ivhich  they  named  the  endurance  limit,  belovr  vhich  fracture 
will  not  occur,  no  matter  hov  often  the   stress  is  repeated.     Their 
conclusion  is,   "For  the  metals  tested  under  reversed   stress  there 
was  observed  a  well-defined  critical   stress  at  which  the  relation 
between  unit   stress  and  the  number  of  reversals  necessary  to  cause 
failure   changed  markedly.     Below  this  critical    stress  the  metals 


Civil  Bngr-8B  Assignment  29  '  Page   11 

withstood  100,000,000  reversals  of   stress,  and,    so  far  as  can  be 
predicted  from  test  results,  vrould  have  withstood  and  indefinite 
number  of   such  reversals.     The  name  endurance   limit  has  been  given 
to  this  critical   stress."     Other  conclusions  will  be  referred  to 
later • 

The  rotating  beam  type  of  machine,    see  Figure  25  on  page  71, 
is  most  commonly  used  in  repeatsd   stress  investigations. 

Effect  o£  heat  treatment:     Read  Article  825.     The  results  of 
the   Illinois  investigation  are    summarized  as  follov/s:     "The  test 
re  sluts  indicate  the  effectiveness  of  proper  heat  treatment  in 
raising  the  endurance   limit  of  the  ferrous  metals  tested.      It   should 
be  noted  that  an  increase   in   static  elastic   strength  due  to  heat 

treatment   is  not  a  reliable  index  of  increase  of  endurance  limit 

rever  se 
under  Astr  ess. 

Effect  of    speed:      In  the   Illinois  tests  the    speed  was  varied 
from  200  to  a  maximum  of  5,000  r.p.m.   and  the  endurance   limit  at 
extreme    speeds  was  not  different  from  that  obtained  for  the    same 
steels  when  tested  at  1,500  r.p.m.     The   information  given  in 
Article   826  is,   therefore,    inaccurate. 

Effect  of   surface  condition  and  change  o£  section:     The   in- 
formation given   in  Article    327  was  confirmed  by  the   Illinois  in- 
vestigation.     "Abrupt  changes  of  outline  of   specimens  subjected  to 
repeated    stress  greatly   lowered  their  resistance.      Cracks,  nicks, 
and  grooves  caused  in  machine  parts  by  wear,  by  accidents.!  blovs, 
by  accidental  heavy  overload,   or  by  improper  heat  treatment  may 


Civil  Engr-8B  Assignment  29  •  Page   12 

cause    such   abrupt   change  of  outline.      Shoulders  with   short  radius 
fillets  are  a  marked   source  of  weakness." 

"poor    surface  finish  on   specimens  subjected  to  reversed   stress 
was  found  to  te  a   source  of  TO  a  lone  ss.     This  weakness  may  be  explained 
by  the  formation  of  cracks  due  to   localized  stress  at  the  bottom 

of    scratches  or  tool  marks." 

with  different  heat  treatments. 
composition:     Alloy    steel  s/\such  as  nickel  and  chrome - 

nickel    steels,  were  used  in  the  Illinois  investigation.     The  re- 
sults  showed  that  the  higher   the  ultimate    strength  the  higher  the 
endurance   limit*     That  is,   if  a  heat  treated  carbon   steel  had  a 
higher  ultimate    strength  than  a  chrome-nickel   steel  the   carbon    steel 
v/ould  also  have  the  higher  endurance   limit. 

Relation  to  elastic   limit  and  ultimate :     Read  Article   829* 
The  conclusion  on  this  subject  from  the  Illinois  investigation  is 
as  follows:      "in  th^econnaissance  tests  made   in  the  field  of 
ferrous  metals  no   simple  relation  was  found  between  the  endurance 
limit  and  the   elastic   limit,  however  determined.     The  ultimate 
tensile    strength   seemed  to  be  a  better   index  of  the  endurance   limit 
under  reversed   stress  than  was  the  elastic   limit.     The  Brinell 
hardness  test    seemed  to  furnish  a   still  better   index  of  the  en- 
durance  limit a"     The  mechanism  of  fatigue  as  viewed  under   the  mi- 
croscope  is  a  phenomenon  of  actual  rupture   -  the   crystal  elements 
slide  on  each  other  and  finally  tear   apart.-   Some  microscopic 
element,    an   individual  crystal,   reaches  its  ultimate    strength  and 
starts  the   crack  which  produces  failure  of  the   entire  piece. 


Civil  Engr-SB  Assignment  29  Page   13 

Under  fatigue   ^here  is  no  flow  of  the  material   such  as  occurs  at 
the  elastic   limit,   and   it    seems  reasonable  that   the   endurance 
limit  is  more  closely  correlated  to  ultimate    strength  than  to 
elastic   limit. 

Te st s  beyond  the  y ie Id  point:     Read  Article  830.     Up  to  the 
present  time  no  mechanical  device  has  been  found  in  which  the 
specimen  can  be    stressed  beyond  the  elastic   limit  at  a  relatively 
small  number  of  reversals  of   stress,    say  less  than  one  million,   and 
the  endurance   limit  thereby  predicted.      In   stress-number  of  rever- 
sal curves  like  those  on  page  775  in  the  text,  the  endurance   limit 
is  clearly   indicated  by  a  decided  break  in  the  curve.     For  all  re- 
versals of   stress  over   10  million  the  curves  in  the   Illinois  tests 
were  horizontal   lines.     The  most  reliable  method  of  determining 
the    strength  to  resist  repeated   loading  is  to  determine   the  endur- 
ance  limit  by  testing  a   series  of   specimens,    subjecting  them  to  re- 
versals of   stresses  of  various  magnitudes,   and  constructing  dia- 
grams based  on   stress  and  number  of  reversals.     The  ultimate 
tensile    strength  and  the  Brine  11  hardness  tests  are   less  reliable 
indices  of  fatigue    strength. 

"Accelerated  or    short-time  tests  of  metals  under  repeated 
stress,  using  high   stresses  and  consequent   small  numbers  of  repeti- 
tions to   cause  failure,    are  not  reliable   as  indices  of  the   ability 
of  metal  to  with  stand  millions  of  repetitions  of  low  stress.  ' 
This  is  one  of  the   important  conclusions  of  the   Illinois  tests. 


Civil-Engr-8B  Assignment  29-  Page  14 

Rapid  determinations  of  fatigue    strength:     Read  Article   831. 
The  rise-in-temperature  method   suggested  by   Stromeyer   (see  page 
778  in  text)  gives  promise  of  becoming  a   satisfactory  commercial 
method  of  determining  the  endurance   limit  of   steel.     Temperature 
measur events  were  made   in  connection  with  the   Illinois  tests  with 
the  following  conclusions:      "The  endurance   limit  for  the  ferrous 
metals  tested  could  be  predicted  v^ith  a  good  degree  of  accuracy  by 
the  measurement  of  rise  of  temperature  under  reversed   stress  ap- 
plied for   a  fev:  minutes."     The  endurance  limit  is  indicated  by  the 
sharp  break  in  the  curve  drawn  between  unit   stress,  and  by  rise  in 
temperature  after   1,000  reversals  of   stress. 

Bauschinger  ls  theory  of  fatigue  failure  as  explained  in 
Article   832  has  never  been  applied  to  recent  test  results.     But 
while   it  does  not   imply  a  change  in  crystalline   structure   such  as 
was  outlined  in  the  erroneous  cold-crystallization  theory,   it  does 
imply  change   in  the   inherent  nature  of  the  material.     The  localized 
stress  theory  proposed  by  Moore  and  Kommers,  therefore,    seems  more 
probable.      "The   effect  of  external  non-homogeneity  due   to   scratches, 
tool  marks,    square    shoulders  and  notches  is  well  known.      Internal 
non -homogeneity  niay  be  due  to  blow-holes,  pipes,    inclusion  of   slag, 
irregularity   of  crystalline    structure   on  account  of  the  presence 
of  two   or  more   constituents  of  varying   strength,  variation  in 
orientation  of   crystals,   or   the  presence   of   initial    stresses  caused 
by  mechanical  7/orking  or  heat  treatment.     Owing  to  the  minute  area 


Civil  Engr-8B  Assignment  29  Page    15 

over  which  it  exists,   this  localized   stress  produces  no  appreciable 
effect  under  a   single   load,   but  under   load  repeated  many  times 
there   is  started  from  this  area  a  microscopic  crack,   at  the  root 
of  which  there  exists  high  localized   stress  -which  under  repetition 
of   stress  spreads  until  it  finally  causes  failure.     Fatigue 
failures  are  not  necessarily  due  to  accidental  flaws  or  irregu- 
larities.     Such  failures  may,   in  practice,   often  be  due  to   such 
causes,   but  the  definiteness  of  the  endurance  limits  points  to  the 
conclusion  that  the  endurance   limit  is  a  property  of  the  material 
just  as  much  as  the  ultimate    strength-      If  failure   is  due  to  flaws, 
these  flaws  are   an  inherent  part  of  the    structure  of  the   steel." 

Articles  832  and  835  inclusive  give  no  information  on  the 
phenomenon  of  fatigue  and   since  the  diagrams  and  formulae  were 
worked  out  on  the   basis  of  incomplete  data  these  articles  may  be 
omitted. 

Endurance   limit   in  terms  of  ultimate  tensile  strength:     The 

following  is  taken  from  the   Illinois  report:      "in  none  of  the 

under 
ferrous  metals  tested  did  the  endurance    limit   completely  reversed 

stress  fall  below  36$  of  the  ultimate  tensile  strength;  for  only 
one  aaetal  did  it  fall  below  40^,  while  for  several  metals  it  was 
more  than  50f0.  However,  these  metals  were  to  a  high  degree  free 
from  inclusions  or  .other  internal  defects;  the  specimens  had  no 
abrupt  changes  of  outline,  and  had  a  good  surface  finish." 

Endurance   limit  under  repeated    stress:      A  reversed    stress  is 
one  that  varies  alternately  from  tension  to   compression.     A  repeated 


•  -.V, 


; : 


Civil  Engr-88  Assignment  29  Page   16 

stress  is  one  which  varies  from  zero  to  a  maximum  either   in  ten- 
sion or   compression.     Recent  experiments  made  at  the  University  of 
Illinois  indicate  that  the  endurance   limit  under  repeated   stress 
is  approximately  1.5  times  that  under  reversed   stress. 

QUESTIONS: 

1.  Define  fatigue* 

2.  What  is  the  theory  of  cold  crystallization  of  steel? 

3.  Is  a  crystalline  fracture  necessarily  the  result  of  brittleness? 

4.  What  causes  the  crystalline  appearance  of  a  fatigue  fracture? 

5.  Explain  the  mechanism  of  fatigue  failure. 

6.  What  is  meant  by  the  term  endurance  limit?  How  can  the  en- 
durance limit  be  determined? 

7.  How  does  heat  treatment  effect  the  endurance  limit  of  steel? 

8.  What  is  the  effect  of  surface  condition  and  change  of  sec- 
tion on  the  endurance  limit  of  steel? 

9.  VJhat  is  tne  best  criterion  of  fatigue  strength  or  so-called 
endurance  limit? 

10.  Can  endurance  limit  be  predicted  by  tests  in  which  the 
specimen  is  stressed  beyond  the  yield  point  of  the  material? 

11.  Discuss  the  value  of  the  rise  in  temperature  of  steel  under 
repeated  stress  as  an  index  of  fatigue  strength. 

12.  What  is  the  relation  between  the  endurance  limit  under  re- 
peated stress  and  reversed  stress? 


-.,"•-     '      v         .•-     . 

*  -    «  -  .        ^. 


UNIVERSITY  0?  CALIFORNIA.  EXTEKaiON  DIVISION 
Correspondence  Courses 

.Materials  of  Engineering  Construction 
Civil  Engr.-8B  Assignment  30  Prof,   C.T.Yttskocil 

THE  CORROSION  OF  METALS 

The   importance  of  corrosion*    -     Study  Article  83V. 
The  rapid  coating  of  the  light-colored  glistening  surface  of 
machined   iron  and  steel  by  a  dull  layer  of  oxide   is  a  familiar 
phenomenon.      Prolonged  exposure  to  air  and  moisture   increases  the 
conversion  of  the  netal  into  a  loosely  coherent  compound     known 

as  rust  r;hich  has  a  dark  reddish-brown  color.     The  formation  of 

unif ore. coat ing  of    , 

a/rust,  is  not  as  injurious  as  the  corrosive  action  known  as  pitting. 

The  corrosion  of  iron  and  steel  usually  occurs  in  the  latter  form, 
in  ivhich  small  deep  holes  are  eaten  into  the  metal.     The   importance 
of  protecting  exposed  ferrous  metals  against  corrosion  has  long 
been  recognized,  but  unfortunately  the  experimental  studies  made 
have   lead  to  contradictory  results  and  hence  there   is  little 
agreement  between  investigators  as  to  the  true  mechanics  of  the 
phenomenon  of  corrosion. 

Corrosion  implies  the  conversion  of  metallic  elements   into 
compounds  which  are  usually  insoluble   in  water.     The  corrosion 
of  iron  and  steel  is  generally  known-  by  the  term  rusting.     Rust, 
which  is  a  hydrated  red-oxide   of  iron,    (Fe2<^*H20)   occupies 
about  ten  times  the  volume   of  the  original  steel.   The  x  in  the 
formula  indicates  that  there   is  a  variable  amount  of  combined 
water  in  rust. 


Oi\-ll  Engr.-SB  -Assignment  30. 


page 


All  metals,  with  the  possible  exception  of  gold,   are  subject 
to  corrosion.      In  the  case   of  steel,  corrosion,  when  once  started, 
continues  until  the  metal  is  destroyed;   but  the  thin  film  of 
o^ids  that  forms  on  the  exposed  surface   of  aluminum  brings 
atmospheric  corrosive  action  to  a  standstill.     Ferrous  metals  are 
protected  by  being  plated  with  nickel,   although  nickel  itself 
corrodes.      It  is  relatively  stable,   however,  because  as  in  the 
case  of  aluminum,  a  surface  film  of  oxide  forms  and  protects 
the  underlying  natal.      Copper   is  also  one  of  the  stable  metals. 
Upon  exposure  to  the  atmosphere  the   surface  of  the  metal  is  rapidly 
converted   into  the  green  basic  carbonate  which  retards  the  cor- 
rosive action. 

In  spite   of  the  fact  that  those  metals  which  resist  corrosion, 
such  as  nickel,  aluminum  and  copper,  become  coated  with  a  filn 
which  prevents  the  actual  contact  between  the  corroding  nedium 
(a  combination  of  air  and  moisture)     and  the  metal,   little     ex- 
perimental work  has  been  done   on  the  formation  of  protecting 
films. 

If  a  protecting  film  is  the   solution  of  the  rust  problem 
it  is  evident  that  it  must  be  a  self-healing  film.      It  will  be 
remembered  that  in  the  case  of  the  preservative  treatment  of 
wood  the  most  effective  method  was  to  maintain  a  perfect  toxic 
coating.      If  this  surface  was  broken  so  as.  to  expose  the  untreated 
vood  the  whole  piece  was  then  subject  to  the  attack  of  fungi 


Civil  Engr.«8B       Assignment  30,  page  3> 

which  could  gain  entrance  at  the  break  in  the  protective  coating. 
Parkerized  iron  resists  corrosion  "because  of  a  film  of  oil  and 
phosphate  but  the  film  must  be  unbroken  to  protect  the  underlying 
matal.   It  is  common  practice  to  paint  or  varnish  metals  to  pro- 
tect them  from  atmospheric  corrosion.   More  durable  protective 
films  are  those  of  zinc,  as  on  galvanized  iron,  and  nickel,  on 
nicks 1 -plated  iron  and  steel.  At  the  present  time  (1922)  all 

authorities  seem  to  agree  that  corrosion  of  iron  will  occur  only 

Irst 
in  the  presence  of  both  water  and  oxygen.  See /statement  to  this 

effect  given  on  page  791  -  the  sentence  in  the  first  paragraph 
of  article  846.   Iron  will  not  rust  in  dry  air.  Furthermore, 
when  submerged  in  v/ater  from  which  all  the  dissolved  oxygen 
has  been  excluded,  iron  will  n6t  rust.  The  water  must  be  placed 
in  a  sealed  tube  which  contains  no  air.   If  the  surface  of  the 
water  is  exposed  to  air  it  will  absorb  cocygen  and  the  immersed 
iron  will  begin  to  rust* 

Variation  in  durability  of  iron.-  Read  Article  838.  The 
remarkable  state  of  preservation  of  the  Pillar  of  Delhi  is  re- 
ferted  to  in  this  article.  Examples  of  buried  cast  iron  water 
mains,  in  which  the  water  is  in  motion,  which  have  withstood 
corrosion  for  long  periods  are  more  numerous  than  examples  of 
exposed  iron  such  as  the  Pillar  of  Delhi.   It  is  quite  evident, 
hov/ever,  that  unprotefcted  exposed  iron  will,  in  occasional  instances 
only,  resist  the  destructive  action  of  atmospheric  corrosion. 
Any  examples  are  noteworthy. 


ttivtl  r_jiig:r.-8B  Assignment  30  Page  4. 

It  should  be  noted  that  the  destruction  of  the  shin 
.ic^aera,   also  referred  to  in  this  article  was  not  due  to  atmo- 
spheric corrosion.      It  is   obvious  that  iron  Trill  be  destroyed  by 
electrolytic  action.     This   is  referred  to  in  Article  843  under 
the   heading  of  local  couples.     Electrolytic  action  is  sometimes 
referred  to  as  galvanic  action.     While  action  of  this  kind  is 
confaon,   many  engineers  do  not  take   into  consederation  its  pre- 
vention in  their  designs,   so  that  replacements  are  necessary.     A 
striking  example   occured  at  the  Panama  Canal  in  the  corrosion  of 
certain  parts  of  the   lock  machinery,  as  noted  in  Article  843. 
Electrolytic  action  was  set  up  between  bronze  and    ..steel  and 
also  betv/een  babbitt  metal  and  cast-steel.     The  bronze  had  to  be 
replaced  and  the  Babbitt  metal  iras  removed  and  Greenheart,  a 
durable  tropical  wood,  was   substituted.     This  tupe   of  corrosion 
-:hich  here   occured,   can  be  prevented  by  preventing  electrolytic 
action.     Dissimilar  metals,    in  the  presence  of  water,  will  always 
be   corroded     when  a  closed     circuit  can  be  established."     TThen  the 
netals  cannot  be  effectively  insulated     a  poor  conductor  must  be 
used.     Bronze  bearings   in  submerged  turbines  would   soon  corrode. 
These  bearings  are  usually  made,   therefore,   of  wood   such  as 
lignum  vitae.     Ele  ctrolytic  action     was  responsible  for  the  de- 
struction of  the  $500,000  yacht  Sea  Call.      As  noted   in  Iron  Age, 
February  1,   1917,  the  plates  of  the  hull    frere  made  of  Monel. 
iietal  and  Mere  fastened  directly  to  the   steel  frame   of  the   ship. 


Civil  Engr.-SB  Assignment  30  Page  5, 

The  contact  of  these  dissimilar  metals  set  up  destructive  eloc- 
t^olytic   action. 

Validity  of  the  acid  test.-  Read  Article  839.      AS  yet  the 
acid  test  has  not  been  developed  so  that  it  can  be  used  as  a 
measure  of  resistance  to  atmospheric  corrosion. 

Relative  corrosion  of  ferrous  metals.-  Read  Article  840. 
Manufacturers  of  wrought  iron  and  steel  widely  advertise  the  rust 
resisting  qualities  of  their  products.      Steel  marketed  under  the 
trade  name  of  ingot  iron  is  advertised  as  being  particularly 
durable.      Few  comparative  tests  have  been  made  by  disinterested 
parties,   so  that  the  relative  durability  of  these  metals  is  not 
accurately  knorm.     Une  relative  rust-resistive  qualities  of 
•ur ought  iron  and   steel  are  therefore  much  disputed. 

Read  Articles  841  to  845   inclusive.      Pitting  and   local 
couples  have  already  been  referred  to.      It  has  been  knoivn  for  a 
long  time  that  dissolved  air  stimulates  corrosion*     The  uncertainty 
as  to  the  true  action  of  atmospheric  corrosion  is  demonstrated 
by  the  varied  practice   of  the  steel  manufacturers.      Some  attempt 
to  secure  the  maximum  purity  r/hile   others,  add  copper,   a  foreign 
metal,    in  the  attempt  to  obtain  increased  durability.      The  com- 
mittee  on  Corrosion  of   Iron  and  Steel  of  the  American  Society 
for  Besting  Materials  have  recently  reported  that,    "copper -bear ing 
metal ; shows  marked  superiority  in  rust-resisting  properties  as 
compared  to  non-copper-bearing  metal  of  substantially  the  same 


Civil  3ngr.-8B       Assignment  30.  page  6. 

general  composition."  It  should  be  noted  that  copper,  in  copper- 
bearing  steels,  is  no  protection  when  the  steels  are  immersed  in 
liquids. 

:iill-scale,  the  black  oxide  of  iron  (Fe^O/),  forms  a  good 
protective  coating,  but  unfortunately  it  is  brittle  and  is  easily 
broken.   If  an  unbroken  layer  could  be  maintained,  no  further  treat- 
ment would  be  necessary.   Since  this  is  impractical  the  best  prac- 
tice is  to  remove  the  mill-scale  before  applying  any  of  the  common 
metal  or  paint  coatings. 

The  Electrolytic  Theory  of  Rusting.-  Read  Article  846. 
The  follor/ing  statement  is  taken  from  Cushman  and  Gardner,  see 
references  listed  at  the  bottom  of  page  787.   "  Iron  has  a  certain 
solution  tension.;  even  -when  the  iron  is  chemically  pure  and  the 
solvent  pure  -water,   the  solution  tension  is  modified  by  impurities 
or  additional  substances  contained  in  the  metal  and  in  the  solvent. 
The  effect  of  the  slightest  segregation  in  the  metal  vill  throw 
the  surface  out  of  equilibrium,  and  the  solution  tension  will  be 
greater  at  some  points  than  at  others.  The  points  or  nodes  of 
maximum  solution  pressure  v/ill  be  electro-positive  to  those  of 
minimum  pressure,  and  a  current  will  flow,  provided  the  surface 
points  are  in  contact,  through  a  conducting  film.   If  the  film  is 
water,  cr  in  any  way  moist,  the  higher  its  conductivity  the  faster 
the  iron  will  pass  into  solution  in  the  electro-positive  areas, 
and  the  faster  the  corrosion  proceeds.   Positive  hydrogen  ions 


Civil  Engr.-3B        Assignment  30.  Page  7. 

migrate  to  the  negative  areas,  negative  hydroxyls  to  the  positives. 

"If  the  concentration  of  the  hydrogen  ions  is  sufficiently 
high,  the  hydrogen  ions  will  exchange  their  electrostatic  charges 
w:th  the  iron  atoms  sweeping  into  solution,  and  gaseous  hydrogen 
is  seen  escaping  from  the  system.   This  takes  place  \vhenever  iron 
is  dissolved  in  an  acid.   If,  however,  as  is  usual  in  ordinary 
rusting,  the  acidity  is  not  high  enough  to  produce  this  result, 
the  hydrogen  ions  r/ill  polarize  to  a  great  extent  around  the 
positive  nodes  vdthout  accomplishing  a  complete  exchange.  This 
polarization  effect  resists  and  slows  dcr.m  action.  Nevertheless, 
some  exchange  takes  place  and  iron  slowly  pushes  through." 

According  to  this  theory  iron  goes  into  solution  as  a 
result  of  electro-chemical  action  similar  to  that  which  occurs 
in  a  simple  form  of  primary  cell. 

Carbonic  acid  theory.-  According  to  this  theory,  which  is 
also  mentioned  in  Article  846,  iron  will  not  rust  without  the 
action  of  carbonic  or  some  other  acid.  This  explanation  of  the 
corrosion  of  iron  is  plausible  but  the  theory  has  been  discredited 
by  investigators  who  have  made  iron  rust  in  water  containing 
oxygen  without  a  trace  of  carbon  dioxide.   In  fact  they  have  made 
iron  corrode  in  slightly  alkaline  solutions  in  which  the  effect 
of  any  acid  v/ould  have  been  neutralized. 

Due  to  the  controversial  status  of  the  subject  of  corrosion 
the  remainder  of  this  chapter  in  the  text  is  not  important.   It 
should  be  read,  however,  and  the  following  points  noted: 


Civil  Sn^r.-SB          Assignment  30.  Page  8. 

The  electrolytic  action  between  strained  and  unstrained 
metal  as  explained  in  Articles  852  and  853  is  sometir.es  of  im- 
portance..  Article  855  on  the  protection  of  iron  and  steel  against 
corrosion  is,  in  a  "way,  repetition,  since  many  of  the  nethods 
mentioned  have  already  "been  referred  to.   Surface  coatings  of  painx 
protect  steel  quite  well  against  atmospheric  corrosion.  Two  thin 
coats  are  better  than  one  thick  one.  The  results  observed  from 
prolonged  exposure  under  v/ater  shor.v  that  painted  steel  is  not 
protected  against  corrosion. 

^.t  one  time,  alkalies  "were  supposed  to  inhibit  corrosion 
but  it  has  been  shov/n  that  weakly  alkaline  solutions  of  many 
salts  induce  corrosion.   It  has  been  found  very  difficult  to 
protect  iron  and  steel  laid  in  alkali  soils  from  the  destructive 
effects  of  pitting. 

The  difference  between  atmospheric  corrosion  and  the  often 
preventable  galvanic  action  between  unlike  metals,  and  corrosion 
caused  by  stray  currents  should  be  recognized. 


Civil  Engr.-83  Assignment  30.  Pa^e  9. 

QUESTIONS 

1.  What   is  rust? 

2.  Yifhat  is  meant  by  corrosion? 

3.  Why  is  pitting  more  destructive  than  a  uniform  coating  cf 
rust? 

4.  Explain  the  reason  for  the  relative  stability  of  aluminum, 
nickel  and  copper  when  subjected  to  atmospheric  corrosion, 

5.  What  is  the  chief  requisite  for  protecting  films? 

6.  Why  do  unlike  netals  such  as  steel  and  bronze  corrode  when 
placed  in  contact  under  water? 

7.  Why  are  submerged  turbine  bearings  made  of  wood? 

8.  Discuss  the  value  cf  copper  in  copper -be a ring  steels  as  a 
means  to  increase  the  durability  of  steel  against  corrosion. 

9.  Give  a  clear  statement  of  the  electrolytic  theory  of  corrosion. 

10.  Explain  the  acid  theory  of  corrosion. 

11.  Why  is  the  acid  theory  an  unsatisfactory  explanation  of  the 
corrosion  of  iron  and  steel? 

12.  What  methods  are  used  to  protect  steel  from  corrosion? 


Civil  Engr.-SB 


Assignment  30. 


Page  10. 
(Special) 


Summary  of  important  physical  properties  of  materials  given  in 
the  order  in  which  they  r:ere  studied.  Approximate  values  given. 


Material 


Compressive 

Strength, 
lb. per   sq, in, 


Ilodulus   of 
Rupture 
lb. per   sq. in 


Modulus  of 
Elasticity, 
lb«  per   sq.  in. 


Granite                                                20,000 

1,500 

8,000,000 

Douglas  Fir   (air  dry) 

(parallel  to  grain)                7,000 

10,000 

1,500,000 

(perpendicular  to  grain)          900 

Building  brick                                      4,000 

1,000 

6,000,000 

Paving  brick                                       10,000 

2,000 

6,000,000 

Hollow  tile   (on  end)                        7,000 

— 

4,000,000 

Portland  cement   (neat)    (6  mo.  )10,000 

1,OCO 



Portland  cement  mortar   1.6           1,000 

300 



(6  no.) 

Gyp  sun                                                   1,500 

400 

1,000,000 

Magnesite   stucco                                 2,700 

Tension       500  ; 

Ftear  3,000,000 

Concrete    (1  to  6  at  28  days)        2,000 

200              —  1 

,000  2,000,000 

Tensile  strength 
lb.  per  sq.  in. 


Elastic 
Unit 


Ult  iuate 


Fr ought   iron                 30,000  50,000 

Steel   (6. 2$;carbon  )  30,000  60,000 

Plo-u   steel  iire          170,000  250,000 

Cast  iron  (gray)*                20,000 

Halleabie  cast   iron  20,000  45,000 

Copper(hot  rolled)        7,000  30,000 

*4uninun  (draT/n)         20,000  30,000 

Iionel  netal  (Rolled)   50,000  85,000 

Brass   (Cast)  50,000 

Bronze  (Cast)                         30,000 


Compressive 
strength  lb, 
per  sq,  in* 


30,000 
30,000 

70,000 
20,000 


percentage     codulus 
elongation  of 

Elastic- 
ity, lb. 
per   sq.in. 


35 

27,000,000 

35 

30,000,000 

5 

30,000,000 

— 

15,000,000 

7 

20,000,000 

50 

—  - 

40 

20,000,000 

30 

13,000,000 

10 

15,000,000 

*;iodulus   of  rupture   45,000   lb.  per- sq.  in. 


YE  03745 


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